Facebook's a fad on steroids that's become a symbol of sitting at a computer too long with no life. Maybe he doesn't want to be your facebook freind out of principle that it feels cheap or annoying or "everyone's doing it"-ish. Whatever he's hiding, if he's hiding anything, let him hide it. If it bothers you too much let it go and move on if it's that important to you. Don't try to suck him into the "plastic crap nobody wants anymore, ostentatious vehicle, reality TV, blackberry, what were you just doing 5 minutes ago because I need to know, OH-My-God-like-whatEver" pop culture consumerism crap unless he has genuine interest in it.
Precious and fragile things
Need special handling
My god, what have we done to you?