The only reason I still have a facebook account is because a friend at the W3C posts interesting stuff there. (Ironically, once of his recurring issues is that we need to take the internet back from the big corporations, yet he's the one keeping me at Facebook.) As soon as he leaves, I will leave too.
A couple of years ago, friends lived abroad for 3 years and used Facebook as their primary means of communication with people back home. I think that was when I started to check Facebook more often. Sometimes every week.