I love Facebook! Having had a Facebook page for about 6 months now I am starting to know all the different things it can do.
Good points about Facebook: keeping in touch with friends I don't see regularly (even got a wedding invite through it), being up to date with Facebook happenings (particularly as my teenage daughter is on it) and Farmville - although many people tell me I'm lame for having a farm.
Bad points about Facebook: Having students send me friend requests (not appropriate!) and online bullying - my daughter has just been through this and it got very nasty.
As a primary school teacher I hear about many children opening Facebook accounts that are not old enough or mature enough to cope with it.