From TechCrunch:
Whoever knows what your interests are right now and can package them up for advertisers has the chance to make a lot of money. Of course, Google does this right now every time you declare your interests in a search box and it offers up matching ads on the side of results. But Facebook and Twitter are trying to capitalize on the shift from search to sharing. Your interests are expressed by what you follow and react to “like,” “retweet,” etc., not only what you explicitly seek out through search.
via Facebook To Twitter: Back Off, We Own People’s Interests.