Facebook doesn't work for me because it seems to be primarily an extension of existing real life social affairs.
I have one, and have 'friends' on it, but most are people I went to school with who I didn't talk to in school...
And family, who I don't talk to regularly..
I post intellectual 'notes', pictures/info of places of historical interest, old coins, insects, etc and nobody notices. Someone posts a pic from the new bar in town, or some inane jabber about partying/being drunk, going to the gym, or changes their 'relationship status' and 20+ comments materialize.
I deleted it at one point, but put it back up because anytime I would run into someone (namely family) they would say "I thought we were friends on Facebook..." (just like the Sout Park episode, I swear) although there was no contact prior to my deletion. It became easier to just have it and let it sit rather than have it deleted (OMGZ, socially unacceptable to not have a facebook!)