By Megan McArdle
Facebook is following you around the Web. You knew that, right?
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.