Demand Media, known as a content farm, produces much of its content on sites like eHow and others in direct response to what it determines people are searching on web, has filed for an IPO, that highlughts on how much it depends on SEO and Google, in particular.
Page 14: Google Funds Big Chunk Of Demand Media: "We've an extensive relationship with Google and a significant portion of our revenue is derived from cost-per-click performance-based advertising provided by Google. For year ended Dec 31, 2009 and six months ended Jun 30, 2010, we derived approximately 18% and 26%, respectively, of our total revenue from our various advertising arrangements with Google."
Page 18: The Importance (And Risk) Of SEO: "Our ability to successfully manage SEO efforts across our owned and operated websites and our customer websites is dependent on timely modification of SEO efforts from time to time in response to periodic changes in search engine algorithms, search query trends and related efforts by providers of search services designed to ensure display of unique offerings in search results. Our failure to successfully manage our SEO strategy could result in a substantial decrease in traffic,[.…]which would result in substantial decreases in conversion rates and repeat business, as well as increased costs if we were to replace free traffic with paid traffic.