Update: Well, I guess there is some value in it -- for an employer:

Who says Facebook is the province of the young? Increasingly, the 30something bosses of naive recent college grads are proving adept at turning the social network against its earliest adopters. Kevin Colvin, an intern at Anglo Irish Bank's North American arm, was busted when he told his manager, Paul Davis, that he'd miss work due to what colleagues took to be a "family emergency". Davis turned up the photo above, freshly posted to Facebook from the Halloween party Colvin apparently missed work to attend, and attached it to his reply, copying the rest of the office as he did it. The email thread is now spreading around the net. After the jump, the entire exchange, and the incriminating photo.

Update: There is a new, well-written informationweek article on social networks by Cory Doctorow, titled How Your Creepy Ex-Co-Workers Will Kill Facebook