One thing I really do like about facebook is the band event thing. I don't run my bands facebook page, but i'm slowly becoming familiar with it. I like the fact that you can announce your gig, and all your friends can say whether they are going. It is a good indicator of audience size, and a really good way to publicise the event.
If you are in a band, this is definately worth doing - I think it has had a positive effect on our audience numbers.
Thanks for all the friend/fan things... will be reciprocating whereever possible