Social networking sites are a fascinating phenomenon. Users create an online persona, including pictures, likes and dislikes, relationship status, and activities. Sometime users tend to provide enough information for their friends to identify them--something like a highschool yearbook entry. Most of us want facebook to be much more--a different model of interpersonal interaction.
Much of what goes on on a site like facebook can be considered, by the cynical among us, signaling behavior--that is, because we have such freedom of choice as to what we include or elide, virtually everything on facebook counts as a personal advertisement. Most native English-speakers have read "Hamlet" once or twice in our lives, but not all of us would include it as a favourite book. For those who do, it serves as a signal, an affiliation, or an invitation. Thanks to attentions from the more quantitatively inclined, "Hamlet" also signals an SAT score in the 1000 range. The idea is to mine the apparently harmless public data facebook collects for various affiliations, like "the 10 favorite books at the University of Toronto," and presume a correlation with other known characteristics of that affiliation, in this case the published average SAT levels. Finally, we can look at our own facebook friends to see if any of them lists "Hamlet" as a favourite book. If they do, then by the improper logic that accompanies all signaling behaviour, their SAT scores must be in the 1000 range. Lolita, One Hundred Years of Solitude, and Crime and Punishment are smarty-pants signals (1300+ SATs), though I imagine that the release of a film for One Hundred Years will be a near-term spoiler.
Most uses of facebook are old-fashioned. We use it to pass notes, whisper rumors, send invitations to parties, flirt, and spy on our friends. Sharing photos, notes, and interests isn't novel, but it is a lot easier on facebook--and it allows interested parties to learn as much or as little as they wish. Facebook status messages are new: they can be passive announcements. "Needs a hug" is certain to get a response.