I think it has a very minor value as a sort of public yearbook. Go in there once a year and put where the heck you live now. I go months without even thinking about it.
Was listening to an NPR talk show yesterday and they were saying studies show FB mostly appeals to narcissists. "Look at me." They were also trying to connect the media culture to youth today, saying that youth today define self based on public utterances rather than by internal metrics or means. The expression they used was, "I facebook, therefore I am." I find this kind of impoverished mentality sad because it denotes a person who cannot find contentment in the self. They apparently get depressed if they are alone. They absolutely must find happiness outside of the self.
Socializing is of course a happy thing to do, but when you cannot go 5 minutes without Tweeting, Facebooking, or yapping mindlessly on a cell phone then the culture has gone too far. Bear in mind this "I facebook therefore I am" culture is partly if not fully the result of long commercial exploitation by corporations wanting to sell services and equipment. I see pop media culture addicts as victims.