Here is a great video on the emergence of large horizontal content sites of the like we have not seen before. Horizontal sites are websites like Wikipedia that are completely broad with no target market, building content without a niche strategy. Laurence Couburn describes the shotgun approach that companies like Demand Media take to dominate the long tail of search results with horizontal search.
Demand Media has created their own algorithm that searches for long tail keywords that they can rank for and profit from by running ads against the content.
Some seo companies make a living with horizontal sites but with large companies entering the fray, the heat will be on for the small guy to look for other ways to get their message out.