Imagine the U.S. Census as conducted by direct marketers – that’s the social graph.
Social networks exist to sell you crap. The icky feeling you get when your friend starts to talk to you about Amway, or when you spot someone passing out business cards at a birthday party, is the entire driving force behind a site like Facebook.
Because their collection methods are kind of primitive, these sites have to coax you into doing as much of your social interaction as possible while logged in, so they can see it. It’s as if an ad agency built a nationwide chain of pubs and night clubs in the hopes that people would spend all their time there, rigging the place with microphones and cameras to keep abreast of the latest trends (and staffing it, of course, with that Mormon bartender).