As Rob and Paddy have said, I think that both are valid but have different uses. Although I don't post much at the moment I check in here every day to see what's happening. I also use FB daily as my friends and family are spreadout around the world and it's far easier to post one pic of the kids horse-riding or riding motocross or just being crazy kids and letting the family get in touch and say 'hey, can I have a good copy of xyz pics pls' than phoning them all up and asking if they want them etc..
That said, it's no substitute for the old fashioned phone call either, but it is very useful.
I'd hate to think just how dis-jointed something like a CA thread would get on Facebook though (when you consider how easily we go off topic here!), it's just not built for that and a forum is still the ideal vehicle.
Right, that's enough boll**ks from me, I'm off for another beer before I run the risk of saying something that could constititute making a serious comment !!!