I'm not on FB, but that's because i'm an unsociable bastard. My wife shows me some comments on it, some of which can be quite cringeworthy.
I was on it for a 6 month spell when i was single. It was bloody brilliant to use when picking up women.
My wife's colleague's wife consistently has FB breaks, which she ensures everyone know about on FB. She'll also check in midway through the hiatus to update people. It's brilliant. :D