How else would Facebook know to serve that panda video straight into your news feed, and leave your college friend's ill-informed rant about Pacific trade deals in the dark bowels of its servers? How else would it know to serve you with 7,000 ads for wedding dress vendors the very day you announce your engagement?
Facebook knows what you like. It knows what you don't like. It probably knows whether you have been naughty or nice, and will be selling that data to Santa this Christmas season.
This bothers many people, especially since Facebook keeps expanding the list of things it knows about you, and the ways it is willing to use that data to make money.
The recent announcement that Facebook would soon target ads using your "likes" and "shares" has triggered some Olympic-level teeth- gnashing from the Electronic Frontier Foundation, because Facebook will get information from you not just when you actually like, "like" something, but when you load a page that has a "like" button on it.