RISK FACTORS

An investment in our Class A common stock involves a high degree of risk. You should carefully consider the following risk factors and all other information contained in this prospectus before purchasing our Class A common stock. Any of these risks could harm our business, results of operations, and financial condition and our prospects. In addition, the trading price of our Class A common stock could decline and you may lose some or all of your investment. See “Special Note Regarding Forward-Looking Statements.”

Risks Related to Our Business

We have incurred significant operating losses in the past and we may not be able to generate sufficient revenue to be profitable over the long term.

Since our inception in December 2004, we have incurred significant net operating losses and, as of December 31, 2010, we had an accumulated deficit of $78.7 million. Although our annual revenues grew from approximately $10.6 million in 2008 to approximately $30.5 million in 2010, we expect that our revenue growth rate will decline in the future as a result of a variety of factors, including the maturation of our business. At the same time, we also expect our costs to increase in future periods as we continue to expend substantial financial resources to develop and expand our business, including on:

These investments may not result in increased revenue or growth in our business. If we fail to continue to grow our revenue and overall business and to manage our expenses, we may continue to incur significant losses in the future and not be able to achieve or maintain profitability.

If real estate and mortgage professionals or other advertisers reduce or end their advertising spending with us and we are unable to attract new advertisers, our business would be harmed.

Our current financial model depends on advertising revenues generated almost entirely through sales to real estate agents and brokerages, mortgage lenders and advertisers in categories relevant to real estate. Our ability to attract and retain advertisers, and ultimately to generate advertising revenue, depends on a number of factors, including:

While real estate agents participating in our subscription-based Premier Agent program generally commit to contract terms of six or 12 months, we do not have long-term contracts with most of our other advertisers. Those advertisers could choose to modify or discontinue their relationships with us with little or no advance notice. In addition, as existing subscriptions for our Premier Agent program expire, we may not be successful in renewing these subscriptions, securing new subscriptions or increasing the amount of revenue we earn for a given

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subscription over time. We may not succeed in capturing a greater share of our advertisers’ spending if we are unable to convince advertisers of the effectiveness or superiority of our products as compared to alternatives, including traditional offline advertising media such as television and newspapers. If current advertisers reduce or end their advertising spending with us and we are unable to attract new advertisers, our advertising revenues and business, results of operations and financial condition would be harmed.

If we do not innovate and provide products and services that are attractive to our users and to our advertisers, our business could be harmed.

Our success depends on our continued innovation to provide products and services that make our website and mobile applications useful for consumers and real estate and mortgage professionals and attractive to our advertisers. As a result, we must continually invest significant resources in research and development in order to improve the attractiveness and comprehensiveness of our products and services and effectively incorporate new Internet and mobile technologies into them. If we are unable to provide products and services that users, including real estate professionals, want to use, then users may become dissatisfied and use competitors’ websites and mobile applications. If we are unable to continue offering innovative products and services, we may be unable to attract additional users and advertisers or retain our current users and advertisers, which could harm our business, results of operations and financial condition.

We may be unable to increase awareness of the Zillow brand cost-effectively, which could harm our business.

We rely heavily on the Zillow brand, which we believe is a key asset of our company. Awareness and perceived quality and differentiation of the Zillow brand are important aspects of our efforts to attract and expand the number of consumers who use our website and mobile applications. Should the competition for awareness and brand preference increase among online real estate information providers, we may not be able to successfully maintain or enhance the strength of our brand. If in the future we choose to engage in a paid advertising campaign to further promote the Zillow brand, such efforts may not be successful. If we are unable to maintain or enhance user and advertiser awareness of our brand cost-effectively, our business, results of operations and financial condition could be harmed.

We are dependent on the real estate industry, and changes to that industry, or declines in the real estate market or increases in mortgage interest rates, could reduce the demand for our products and services.

Our financial prospects are significantly dependent on real estate shoppers using our services. Real estate shopping patterns depend on the overall health of the real estate market, which has been in decline since 2007. Changes to the regulation of the real estate industry, including mortgage lending, may negatively impact the prevalence of home ownership. Changes to the real estate industry, declines in the real estate market or increases in mortgage interest rates could reduce demand for our services. Real estate markets also may be negatively impacted by a significant natural disaster, such as earthquake, fire, flood or other disruption.

We may be unable to maintain or establish relationships with real estate brokerages, real estate listing aggregators, multiple listing services, apartment management companies, home builders and other third-party listing providers, which could limit the information we are able to provide to our users.

Our ability to attract users to our website and mobile applications depends to some degree on providing a robust number of for sale and rental listings. To provide these listings, we maintain relationships with real estate brokerages, real estate listing aggregators, multiple listing services, apartment management companies, home builders, other third-party listing providers, and homeowners and their real estate agents to include listing data in our services. Many of our agreements with real estate listing providers are short-term agreements that may be terminated with limited notice. The loss of some of our existing relationships with listing providers, whether due to termination of agreements or otherwise, or an inability to continue to add new listing providers, may cause our listing data to omit information important to users of our products and services. This could reduce user

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confidence in the sale and rental data we provide and make us less popular with consumers, which could harm our business, results of operations and financial condition.

We may be unable to maintain or establish relationships with data providers, which could limit the information we are able to provide to our users and impair our ability to attract or retain users.

We use data under license from certain third-party providers in order to enable the development, maintenance and improvement of our information services, including Zestimates and Rent Zestimates and our living database of homes. We have invested significant time and resources to develop proprietary algorithms, valuation models, software and practices to use and improve upon this specific data. We may be unable to renew our licenses with these data providers, or we may be able to do so only on terms that are less favorable to us, which could harm our ability to continue to develop, maintain and improve these information services and could harm our business, results of operations and financial condition.

We may in the future be subject to disputes regarding the accuracy of our Zestimates and Rent Zestimates.

We provide our users with Zestimate and Rent Zestimate home and rental valuations. A Zestimate is our estimated current market value of a home based on proprietary automated valuation models that apply advanced algorithms to analyze our data; it is not an appraisal. A Rent Zestimate is our estimated current monthly rental price of a home, using similar automated valuation models that we have designed to address the unique attributes of rental homes. From time to time, users disagree with our Zestimates and Rent Zestimates. Any such disagreements could result in distraction from our business or potentially harm our reputation and could result in legal disputes.

We face competition to attract consumers to our website and mobile applications, which could impair our ability to continue to grow the number of users who use our website and mobile applications, which would harm our business, results of operations and financial condition.

Our success depends on our ability to continue to attract additional consumers to our website and mobile applications. Our existing and potential competitors include companies that operate, or could develop, national and local real estate and mortgage websites. These companies could devote greater technical and other resources than we have available, have a more accelerated time frame for deployment and leverage their existing user bases and proprietary technologies to provide products and services that consumers might view as superior to our offerings. Any of our future or existing competitors may introduce different solutions that attract consumers or provide solutions similar to our own but with better branding or marketing resources. If we are unable to continue to grow the number of consumers who use our website and mobile applications, our business, results of operations and financial condition would be harmed.

We may be unable to compete successfully against our existing or future competitors in attracting advertisers, which could harm our business, results of operations and financial condition.

We compete to attract advertisers with media sites, including websites dedicated to providing real estate and mortgage information and services to real estate professionals and consumers, and major Internet portals, general search engines and social media sites, as well as other online companies. We also compete for a share of advertisers’ overall marketing budgets with traditional media such as television, magazines, newspapers and home/apartment guide publications, particularly with respect to advertising dollars spent at the local level by real estate professionals to advertise their qualifications and listings. Large companies with significant brand recognition have large numbers of direct sales personnel and substantial proprietary advertising inventory and web traffic, which may provide a competitive advantage. To compete successfully for advertisers against future and existing competitors, we must continue to invest resources in developing our advertising platform and proving the effectiveness and relevance of our advertising products and services. Pressure from competitors seeking to acquire a greater share of our advertisers’ overall marketing budget could adversely affect our pricing

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and margins, lower our revenue, and increase our research and development and marketing expenses. If we are unable to compete successfully against our existing or future competitors, our business, financial condition or results of operations would be harmed.

Our dedication to making decisions based primarily on the best interests of consumers may cause us to forgo short-term gains.

Our guiding principle is to build our business by making decisions based primarily upon the best interests of consumers, which we believe has been essential to our success in increasing our user growth rate and engagement and has served the long-term interests of our company and our shareholders. In the past, we have forgone, and we will in the future forgo, certain expansion or short-term revenue opportunities that we do not believe are in the best interests of consumers, even if such decisions negatively impact our results of operations in the short term. In addition, our philosophy of putting consumers first may negatively impact our relationships with our existing or prospective advertisers. This could result in a loss of advertisers which could harm our revenue and results of operations. Our principle of making decisions based primarily upon the best interests of consumers may not result in the long-term benefits that we expect, in which case our user traffic and engagement, business and results of operations could be harmed.

If we fail to manage our growth effectively, our brand, results of operations and business could be harmed.

We have experienced rapid growth in our headcount and operations, which places substantial demand on management and our operational infrastructure. Most of our employees have been with us for fewer than two years. As we continue to grow, we must effectively integrate, develop and motivate a large number of new employees, while maintaining the beneficial aspects of our company culture. In particular, we intend to pursue strategic opportunities and make substantial investments in our technology and development and sales and marketing organizations. If we do not manage the growth of our business and operations effectively, the quality of our services and efficiency of our operations could suffer, which could harm our brand, results of operations and overall business.

If use of the Internet and mobile technology, particularly with respect to online real estate products and services, does not continue to increase as rapidly as we anticipate, our business could be harmed.

Our future success is substantially dependent on the continued use of the Internet and mobile technology as effective media of business and communication by our consumers. Internet and mobile technology use may not continue to develop at historical rates, and consumers may not continue to use the Internet or mobile technology as media for information exchange. Further, these media may not be accepted as viable long-term outlets for information for a number of reasons, including actual or perceived lack of security of information and possible disruptions of service or connectivity. If consumers begin to access real estate information through other media and we fail to innovate, our business may be negatively impacted.

We rely on the performance of highly skilled personnel, and if we are unable to attract, retain and motivate well-qualified employees, our business could be harmed.

We believe our success has depended, and continues to depend, on the efforts and talents of our management and our highly skilled team of employees, including our software engineers, statisticians, marketing professionals and advertising sales staff. Our future success depends on our continuing ability to attract, develop, motivate and retain highly qualified and skilled employees. The loss of any of our senior management or key employees could materially adversely affect our ability to build on the efforts they have undertaken and to execute our business plan, and we may not be able to find adequate replacements. We cannot ensure that we will be able to retain the services of any members of our senior management or other key employees. We do not maintain any key person life insurance policies. If we do not succeed in attracting well-qualified employees or retaining and motivating existing employees, our business could be harmed.

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Any significant disruption in service on our website or in our network could damage our reputation and result in a loss of users of our products and services and of advertisers, which could harm our business, results of operations and financial condition.

Our brand, reputation and ability to attract users and advertisers depend on the reliable performance of our network infrastructure and content delivery processes. We have experienced minor interruptions in these systems in the past, including server failures that temporarily slowed the performance of our website and mobile applications, and we may experience interruptions in the future. Interruptions in these systems, whether due to system failures, computer viruses or physical or electronic break-ins, could affect the security or availability of our products and services on our website and mobile applications and prevent or inhibit the ability of users to access our services. Problems with the reliability or security of our systems could harm our reputation, result in a loss of users of our products and services and of advertisers and result in additional costs, any of which could harm our business, results of operations and financial condition.

Substantially all of the communications, network and computer hardware used to operate our website are located at facilities in the area. We do not own or control the operation of these facilities. Our systems and operations are vulnerable to damage or interruption from fire, flood, power loss, telecommunications failure, terrorist attacks, acts of war, electronic and physical break-ins, computer viruses, earthquakes and similar events. The occurrence of any of the foregoing events could result in damage to our systems and hardware or could cause them to fail completely, and our insurance may not cover such events or may be insufficient to compensate us for losses that may occur.

A failure of our systems at one site could result in reduced functionality for our users, and a total failure of our systems could cause our website or mobile applications to be inaccessible. Problems faced by our third-party web hosting providers with the telecommunications network providers with which they contract or with the systems by which they allocate capacity among their customers, including us, could adversely affect the experience of our users. Our third-party web hosting providers could decide to close their facilities without adequate notice. Any financial difficulties, such as bankruptcy reorganization, faced by our third-party web hosting providers or any of the service providers with whom they contract may have negative effects on our business, the nature and extent of which are difficult to predict. If our third-party web hosting providers are unable to keep up with our growing needs for capacity, this could harm our business.

We do not carry business interruption insurance sufficient to compensate us for the potentially significant losses, including the potential harm to the future growth of our business that may result from interruptions in our service as a result of system failures. Any errors, defects, disruptions or other performance problems with our services could harm our reputation and harm our business, results of operations and financial condition.

We may make acquisitions and investments, which could result in operating difficulties, dilution and other harmful consequences.

We expect to evaluate a wide array of potential strategic opportunities. For example, in March 2011, we acquired the operating assets of a real estate agent and rental property manager marketing service. Any transactions that we enter into could be material to our financial condition and results of operations. The process of integrating an acquired company, business or technology could create unforeseen operating difficulties and expenditures. The areas where we face risks include:

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Our failure to address these risks or other problems encountered in connection with our past or future acquisitions and investments could cause us to fail to realize the anticipated benefits of such acquisitions or investments, incur unanticipated liabilities and harm our business, results of operations and financial condition.

We are subject to a variety of federal and state laws, many of which are unsettled and still developing and which could subject us to claims or otherwise harm our business.

We are subject to a variety of federal and state laws that are continuously evolving and developing, including laws regarding the real estate and mortgage industries, Internet-based businesses and businesses that rely on advertising. These laws can be costly to comply with, can require significant management time and effort, and can subject us to claims or other remedies. These laws may conflict with each other and if we comply with the laws of one jurisdiction, we may find that we are violating laws of another jurisdiction. Additionally, our ability to provide a specific target audience to advertisers is a significant competitive advantage. Any legislation reducing this ability would have a negative impact on our business and results of operations.

If we are unable to comply with these laws or regulations, if we become liable under these laws or regulations or if unfavorable regulations or unfavorable interpretations of existing regulations by courts or regulatory bodies are implemented, we could be directly harmed and forced to implement new measures to reduce our exposure to this liability and it could cause the development of product or service offerings in affected markets to become impractical. This may require us to expend substantial resources or to discontinue certain products or services, limit our ability to expand our product and services offerings or expand into new markets or otherwise harm our business, results of operations and financial condition. In addition, the increased attention focused upon liability issues as a result of lawsuits and legislative proposals could harm our reputation or otherwise impact the growth of our business. Any costs incurred as a result of this potential liability could harm our business and results of operations.

We assist with the processing of customer credit card transactions which results in us receiving personally identifiable information. This information is increasingly subject to legislation and regulation in the United States. This legislation and regulation is generally intended to protect the privacy and security of personal information, including credit card information, that is collected, processed and transmitted. We could be adversely affected if government regulations require us to significantly change our business practices with respect to this type of information.

We may be unable to continue to use the domain names that we use in our business, or prevent third parties from acquiring and using domain names that infringe on, are similar to, or otherwise decrease the value of our brand or our trademarks or service marks.

We have registered domain names for our website that we use in our business, such as Zillow.com. If we lose the ability to use a domain name, we may incur significant expenses to market our products and services under a new domain name, which could harm our business. In addition, our competitors could attempt to capitalize on our brand recognition by using domain names similar to ours. Domain names similar to ours have been registered in the United States and elsewhere. We may be unable to prevent third parties from acquiring and using domain names that infringe on, are similar to, or otherwise decrease the value of our brand or our trademarks or service marks. Protecting and enforcing our rights in our domain names and determining the rights of others may require litigation, which could result in substantial costs and diversion of management’s attention.

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We may be unable to adequately protect our intellectual property, which could harm the value of our brand and our business.

We regard our intellectual property as critical to our success, and we rely on trademark, copyright and patent law, trade secret protection and contracts to protect our proprietary rights. If we are not successful in protecting our intellectual property, the value of our brand and our business, results of operations and financial condition could be harmed.

While we believe that our issued patents and pending patent applications help to protect our business, there can be no assurance that our operations do not, or will not, infringe valid, enforceable patents of third parties or that competitors will not devise new methods of competing with us that are not covered by our patents or patent applications. There also can be no assurance that our patent applications will be approved, that any patents issued will adequately protect our intellectual property, that such patents will not be challenged by third parties or found to be invalid or unenforceable or that our patents will be effective in preventing third parties from utilizing a “copycat” business model to offer the same products or services. Moreover, we rely on intellectual property and technology developed or licensed by third parties, and we may not be able to obtain licenses and technologies from these third parties on reasonable terms or at all.

Effective trademark, service mark, copyright and trade secret protection may not be available in every country in which our products and services may be provided. The laws of certain countries do not protect proprietary rights to the same extent as the laws of the United States and, therefore, in certain jurisdictions, we may be unable to protect intellectual property and our proprietary technology adequately against unauthorized third-party copying or use, which could harm our competitive position. We have licensed in the past, and expect to license in the future, certain of our proprietary rights, such as trademarks or copyrighted material, to third parties. These licensees may take actions that might diminish the value of our proprietary rights or harm our reputation, even if we have agreements prohibiting such activity. To the extent third parties are obligated to indemnify us for breaches of our intellectual property rights, these third parties may be unable to meet these obligations. Any of these events could harm our business, results of operations or financial condition.

Intellectual property disputes are costly to defend and could harm our business, results of operations, financial condition and reputation.

From time to time, we face allegations that we have infringed the trademarks, copyrights, patents and other intellectual property rights of third parties. We are currently subject to patent infringement claims. These claims allege, among other things, that aspects of our technology infringe upon the plaintiffs’ patents. If we are not successful in defending ourselves against these claims, we may be required to pay damages and may be subject to injunctions, each of which could harm our business, results of operations, financial condition and reputation. We may be subject to future claims or allegations relating to our intellectual property rights. As we grow our business and expand our operations we expect that we will continue to be subject to intellectual property claims and allegations. Patent and other intellectual property disputes or litigation may be protracted and expensive, and the results are difficult to predict and may require us to stop offering certain products, services or features, purchase licenses which may be expensive to procure or modify our products or services. In addition, patent or other intellectual property disputes or litigation may result in significant settlement costs. Any of these events could harm our business, results of operations, financial condition and reputation.

In addition, we use open source software in our services and will continue to use open source software in the future. From time to time, we may be subject to claims brought against companies that incorporate open source software into their products or services, claiming ownership of, or demanding release of, the source code, the open source software and/or derivative works that were developed using such software, or otherwise seeking to enforce the terms of the applicable open source license. These claims could also result in litigation, require us to purchase a costly license or require us to devote additional research and development resources to changing our products or services, any of which would have a negative effect on our business and results of operations.

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Even if these matters do not result in litigation or are resolved in our favor or without significant cash settlements, the time and resources necessary to resolve them could harm our business, results of operations, financial condition and reputation.

Confidentiality agreements with employees and others may not adequately prevent disclosure of trade secrets and other proprietary information.

In order to protect our technologies and processes, we rely in part on confidentiality agreements with our employees, licensees, independent contractors and other advisors. These agreements may not effectively prevent disclosure of confidential information, including trade secrets, and may not provide an adequate remedy in the event of unauthorized disclosure of confidential information. In addition, others may independently discover our trade secrets and proprietary information, and in such cases we could not assert any trade secret rights against such parties. To the extent that our employees, contractors or other third parties with whom we do business use intellectual property owned by others in their work for us, disputes may arise as to the rights in related or resulting know-how and inventions. The loss of trade secret protection could make it easier for third parties to compete with our products by copying functionality. In addition, any changes in, or unexpected interpretations of, intellectual property laws may compromise our ability to enforce our trade secret and intellectual property rights. Costly and time-consuming litigation could be necessary to enforce and determine the scope of our proprietary rights, and failure to obtain or maintain protection of our trade secrets or other proprietary information could harm our business, results of operations, reputation and competitive position.

We may be unable to halt the operations of websites that aggregate or misappropriate our data.

From time to time, third parties have misappropriated our data through website scraping, robots or other means and aggregated this data on their websites with data from other companies. In addition, copycat websites have misappropriated data on our network and attempted to imitate our brand or the functionality of our website. When we have become aware of such websites, we have employed technological or legal measures in an attempt to halt their operations. However, we may be unable to detect all such websites in a timely manner and, even if we could, technological and legal measures may be insufficient to halt their operations. In some cases, particularly in the case of websites operating outside of the United States, our available remedies may not be adequate to protect us against the impact of the operation of such websites. Regardless of whether we can successfully enforce our rights against the operators of these websites, any measures that we may take could require us to expend significant financial or other resources, which could harm our business, results of operations or financial condition. In addition, to the extent that such activity creates confusion among consumers or advertisers, our brand and business could be harmed.

If our security measures are compromised, consumers may curtail use of our products and services and advertisers may reduce their advertising on our website.

Our products and services involve the storage and transmission of users’ information, some of which may be private, and security breaches could expose us to a risk of loss or exposure of this information, which could result in potential liability and litigation. For example, a hacker could steal a user’s profile password and manipulate information about that user’s home or post to a forum while posing as that user. Like all websites, our website is vulnerable to computer viruses, break-ins, phishing attacks, attempts to overload our servers with denial-of-service or other attacks and similar disruptions from unauthorized use of our computer systems, any of which could lead to interruptions, delays, or website shutdowns, causing loss of critical data or the unauthorized disclosure or use of personal or other confidential information. If we experience compromises to our security that result in website performance or availability problems, the complete shutdown of our website, or mobile applications, or the loss or unauthorized disclosure of confidential information, our users and advertisers may lose trust and confidence in us, and users may decrease the use of our website or stop using our website in its entirety, and advertisers may decrease or stop advertising on our website. Further, outside parties may attempt to fraudulently induce employees, users or advertisers to disclose sensitive information in order to gain access to

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our information or our users’ or advertisers’ information. Because the techniques used to obtain unauthorized access, disable or degrade service, or sabotage systems change frequently, often are not recognized until launched against a target and may originate from less regulated and remote areas around the world, we may be unable to proactively address these techniques or to implement adequate preventative measures. Any or all of these issues could negatively impact our ability to attract new users and increase engagement by existing users, cause existing users to curtail or stop use of our products or services or close their accounts, cause existing advertisers to cancel their contracts, or subject us to third-party lawsuits, regulatory fines or other action or liability, thereby harming our business, results of operations and financial condition.

We are subject to a number of risks related to credit card and debit card payments we accept.

We accept payments through credit and debit card transactions. For credit and debit card payments, we pay interchange and other fees, which may increase over time. An increase in those fees would require us to either increase the prices we charge or suffer an increase in our operating expenses, either of which could harm our business, financial condition and results of operations.

We depend on processing vendors to complete credit and debit card transactions. If we or our processing vendors fail to maintain adequate systems for the authorization and processing of credit card transactions, it could cause one or more of the major credit card companies to disallow our continued use of their payment products. In addition, if these systems fail to work properly and, as a result, we do not charge our customers’ credit cards on a timely basis or at all, our business, revenue, results of operations and financial condition could be harmed.

We are also subject to payment card association operating rules, certification requirements and rules governing electronic funds transfers, which could change or be reinterpreted to make it more difficult for us to comply. We are required to comply with payment card industry security standards. Failing to comply with those standards may violate payment card association operating rules, federal and state laws and regulations, and the terms of our contracts with payment processors. Any failure to comply fully also may subject us to fines, penalties, damages and civil liability, and may result in the loss of our ability to accept credit and debit card payments. Further, there is no guarantee that such compliance will prevent illegal or improper use of our payment systems or the theft, loss, or misuse of data pertaining to credit and debit cards, card holders and transactions.

If we fail to adequately control fraudulent credit card transactions, we may face civil liability, diminished public perception of our security measures and significantly higher credit card-related costs, each of which could harm our business, results of operations and financial condition.

If we are unable to maintain our chargeback rate or refund rates at acceptable levels, our processing vendors may increase our transaction fees or terminate their relationships with us. Any increases in our credit and debit card fees could harm our results of operations, particularly if we elect not to raise our rates for our service to offset the increase. The termination of our ability to process payments on any major credit or debit card would significantly impair our ability to operate our business.

We expect our results of operations to fluctuate on a quarterly and annual basis.

Our revenue and results of operations could vary significantly from quarter to quarter and year to year and may fail to match our past performance because of a variety of factors, some of which are outside our control. Any of these events could cause the market price of our Class A common stock to fluctuate. Factors that may contribute to the variability of our results of operations include:

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Risks Related to Ownership of Our Class A Common Stock and this Offering

Our securities have no prior market and an active trading market may not develop, which may cause our Class A common stock to trade at a discount from the initial public offering price.

Prior to this offering, there has been no public market for our Class A common stock. The initial public offering price for our Class A common stock will be determined through negotiations between us and the representatives of the underwriters and may not be indicative of the market price of our Class A common stock after this offering. If you purchase shares of our Class A common stock, you may not be able to resell those shares at or above the initial public offering price. We cannot predict the extent to which investor interest in us will lead to the development of an active trading market, or how liquid that market might become. An active public market for our Class A common stock may not develop or be sustained after this offering. If an active public market does not develop or is not sustained, it may cause our Class A common stock to trade at a price lower than the initial public offering price and it may be difficult for you to sell your shares of Class A common stock at a price that is attractive to you.

The dual class structure of our common stock as contained in our charter documents has the effect of concentrating voting control with our founders, and may limit your ability to influence corporate matters.

Our Class B common stock has 10 votes per share, and our Class A common stock, which is the stock we are offering in this offering and the concurrent private placement, has one vote per share. All shares of Class B common stock are held by our founders, Richard Barton and Lloyd Frink. Mr. Barton and Mr. Frink will control approximately         % and         %, respectively, of the aggregate number of shares of our outstanding Class A common stock and Class B common stock, representing approximately         % and         %, respectively, of the voting power of our outstanding capital stock following this offering and the concurrent private placement. Therefore, Mr. Barton and Mr. Frink will have significant control over our management and affairs and over all matters requiring shareholder approval, including the election of directors and significant corporate transactions, such as a merger or other sale of us or our assets, for the foreseeable future. Mr. Barton and Mr. Frink, as the

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holders of Class B common stock, together will be able to control all matters submitted to our shareholders for approval. This concentrated control may limit the ability of holders of our Class A common stock to influence corporate matters for the foreseeable future, and might harm the market price of our Class A common stock by delaying, deferring or preventing a change of control, impeding a merger, consolidation, takeover or other business combination involving us, or discouraging a potential acquirer from acquiring our Class A common stock due to the limited voting power of such stock relative to the Class B common stock.

Our stock price may be volatile, and you may be unable to sell your shares at or above the offering price.

The initial public offering price for the shares of our Class A common stock will be determined by negotiations between us and the representatives of the underwriters and may not be indicative of prices that will prevail in the trading market. The market price of our Class A common stock could be subject to wide fluctuations in response to many of the risk factors discussed in this prospectus, and others beyond our control, including:

Furthermore, the stock markets in recent years have experienced extreme price and volume fluctuations that have affected and continue to affect the market prices of the equity securities of many companies. These fluctuations often have been unrelated or disproportionate to the operating performance of those companies. These broad market and industry fluctuations, as well as general economic, political and market conditions such as recessions, interest rate changes or international currency fluctuations, may negatively impact the market price of our Class A common stock. If the market price of our Class A common stock after this offering does not exceed the initial public offering price, you may not realize any return on your investment in us and may lose some or all of your investment. In the past, companies that have experienced volatility in the market price of their stock have been subject to securities class action litigation. We may be the target of this type of litigation in the future. Securities litigation against us could result in substantial costs and divert management’s attention from other business concerns, which could harm our business, results of operations or financial condition.

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Future sales of our Class A common stock in the public market could cause our stock price to decline.

Sales of a substantial number of shares of our Class A common stock in the public market after this offering, or the perception that such sales might occur, could depress the market price of our Class A common stock and could impair our ability to raise capital through the sale of additional equity securities. Upon completion of this offering and the concurrent private placement, based on our shares outstanding as of December 31, 2010, and after giving effect to the conversion of all outstanding shares of our convertible preferred stock and Class C common stock into shares of Class A common stock, we will have                  shares of Class A common stock outstanding and 32,205,715 shares of Class B common stock outstanding, assuming no exercise of the underwriters’ over-allotment option to purchase additional shares and no exercise of outstanding options.

Of the outstanding shares, all of the shares of Class A common stock sold in this offering will be freely tradable, except that any shares held or acquired by our “affiliates,” as that term is defined in Rule 144 under the Securities Act of 1933, as amended, or the Securities Act, will be subject to the volume limitations and certain other restrictions of Rule 144. The shares to be sold in the concurrent private placement are subject to the holding period requirements of Rule 144 and are, therefore, subject to a minimum six-month holding requirement before such shares can be sold in a non-registered transaction. The remaining              shares of Class A common stock outstanding after this offering and the concurrent private placement (based on our shares outstanding as of December 31, 2010) and the              shares sold in the concurrent private placement will be restricted as a result of securities laws, lock-up agreements or other contractual restrictions that restrict transfers for at least 180 days after the date of this prospectus, subject to certain extensions and subject to certain earlier releases if certain conditions are met. For further information, see “Shares Eligible for Future Sale.” In addition, Citi may, in its sole discretion, release all or some portion of the shares subject to lock-up agreements prior to expiration of the lock-up period. After this offering and the concurrent private placement, the holders of              shares of Class A common stock and 32,205,715 shares of Class B common stock, or         % of our total outstanding Class A common stock (calculated on an as-if-converted basis), based on shares outstanding as of December 31, 2010, will be entitled to rights with respect to registration of these shares under the Securities Act pursuant to an investors’ rights agreement. If the holders of our Class A common stock and Class B common stock entitled to registration rights elect to exercise such rights and sell a large number of shares, they could adversely affect the market price of our Class A common stock. If we file a registration statement for the purposes of selling additional shares to raise capital and are required to include shares held by these holders pursuant to the exercise of their registration rights, our ability to raise capital may be impaired. We intend to file a registration statement on Form S-8 under the Securities Act to register approximately              million shares of our Class A common stock for issuance under our Amended and Restated 2005 Equity Incentive Plan and 2011 Incentive Plan. Once we register these shares, they can be freely sold in the public market when the options underlying the shares are exercised and the shares of Class A common stock are issued, subject to the lock-up period and other restrictions provided under the terms of the applicable plan, option agreements or lock-up agreements entered into with the option holders.

Because the initial public offering price of our Class A common stock will be substantially higher than the pro forma net tangible book value per share of our outstanding Class A and Class B common stock following this offering, new investors will experience immediate and substantial dilution.

The initial public offering price per share will be substantially higher than the pro forma net tangible book value per share of our Class A and Class B common stock immediately following this offering and the concurrent private placement based on the total value of our tangible assets less our total liabilities. Therefore, if you purchase shares of our Class A common stock in this offering, you will experience immediate dilution of $             per share, the difference between the price per share you pay for our Class A common stock and its pro forma net tangible book value per share as of December 31, 2010, after giving effect to the issuance of                  shares of our Class A common stock in this offering and the concurrent private placement. Furthermore, investors purchasing shares of our Class A common stock in this offering will only own approximately         % of our outstanding shares of Class A and Class B common stock (and have         % of the combined voting power of the outstanding shares of our Class A and Class B common stock), after the offering even though their aggregate investment will represent         % of the total consideration received by us in connection with all initial sales of                  shares of our capital stock outstanding as of December 31, 2010, after giving effect to the issuance of

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shares of our Class A common stock in this offering and the concurrent private placement. To the extent outstanding options to purchase our Class A common stock are exercised, investors purchasing our Class A common stock in this offering will experience further dilution.

If securities or industry analysts do not publish research or publish inaccurate or unfavorable research about our business, our stock price and trading volume could decline.

The trading market for our Class A common stock will depend in part on the research and reports that securities or industry analysts publish about our company. We do not currently have and may never obtain research coverage by securities and industry analysts. If few or no securities or industry analysts cover our company, the market price of our Class A common stock could be negatively impacted. If securities or industry analysts cover us and if one or more of such analysts downgrades our Class A common stock or publishes inaccurate or unfavorable research about our business, our stock price would likely decline. If one or more of the analysts covering us fail to publish reports on us regularly, demand for our Class A common stock could decline, which could cause our stock price and trading volume to decline.

The requirements of being a public company may strain our resources and distract our management, which could make it difficult to manage our business.

Following the completion of this offering, we will be required to comply with various regulatory and reporting requirements, including those required by the Securities and Exchange Commission, or the SEC. Complying with these reporting and other regulatory requirements will be time-consuming and will result in increased costs to us and could harm our business, results of operations and financial condition.

As a public company, we will be subject to the reporting requirements of the Securities Exchange Act of 1934, as amended, or the Exchange Act. These requirements could strain our systems and resources. The Exchange Act requires that we file annual, quarterly and current reports with respect to our business and financial condition. The Exchange Act requires that we maintain effective disclosure controls and procedures and internal control over financial reporting. To maintain and improve the effectiveness of our disclosure controls and procedures and internal control over financial reporting, we will need to commit significant resources, hire additional staff and provide additional management oversight. We will be implementing additional procedures and processes for the purpose of addressing the standards and requirements applicable to public companies. Sustaining our growth also will require us to commit additional management, operational and financial resources to identify new professionals to join us and to maintain appropriate operational and financial systems to adequately support expansion. These activities may divert management’s attention from other business concerns and could make it difficult to manage our business, which could harm our business, results of operations, financial condition and cash flows. In addition, if we find any material weakness in our internal control, we could lose investor confidence in the accuracy and completeness of our financial reports, which would cause the market price of our Class A common stock to decline.

Anti-takeover provisions in our charter documents and under Washington law could make an acquisition of us more difficult, limit attempts by our shareholders to replace or remove our current management and limit the market price of our Class A common stock.

Provisions in our articles of incorporation and bylaws, as amended and restated in connection with this offering, may have the effect of delaying or preventing a change of control or changes in our management. Our amended and restated articles of incorporation and amended and restated bylaws will include provisions that:

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These provisions may frustrate or prevent any attempts by our shareholders to replace or remove our current management by making it more difficult for shareholders to replace members of our board of directors, which is responsible for appointing our management. In addition, because we are incorporated in the State of Washington, we are governed by the provisions of Chapter 23B.19 of the Washington Business Corporation Act, which prohibits certain business combinations between us and certain significant shareholders unless specified conditions are met. These provisions may also have the effect of delaying or preventing a change of control of our company, even if this change of control would benefit our shareholders. See “Description of Capital Stock.”

Our management will have broad discretion over the use of the net proceeds we receive in this offering and the proceeds we receive in the concurrent private placement, and might not apply the proceeds in ways that increase the value of your investment.

Our management will have considerable discretion in applying the net proceeds we receive in this offering and the proceeds we receive in the concurrent private placement. We currently intend to use these proceeds primarily for general corporate purposes, including working capital, sales and marketing activities, general and administrative matters and capital expenditures. If appropriate opportunities arise, we may use a portion of these proceeds to acquire or invest in technologies, solutions or businesses that complement our business. We have not allocated these proceeds for any specific purposes. Until these proceeds are used, we plan to invest them, and these investments may not yield a favorable rate of return. If we do not invest or apply these proceeds in ways that enhance shareholder value, we may fail to achieve expected financial results, which could cause our stock price to decline.

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