What facebook is doing here is similar to back when the bigger search engines got in hot water for mixing ads into search results in various shady ways (recall Paid Inclusion programs about 10 years ago, see http://www.wired.com/techbiz/media/news/2004/07/64092 ). It did not benefit the user and generally created confusion and a poor user experience, driving many users to try Google for the first time (Google never had Paid Inclusion that I can recall).