I got invited for FB a year ago and I joined, for about a week. Next I knew, I got all kind of emails from complete strangers saying things like: just going out for a coffee/oo, I am so down.......etc etc
As I was absolutely baffled by all these messages, and didn't have much time; I decided FB was not my thing.
It took me a few hours/weeks to delete my account; it behaved like a kind of virus.
Perhaps its a generation thing. My daughter (21) just loves it.