For me Facebook is kind of a collection of people who I've bumbed into during the years. There's a people as "my friends" who in real life I might not even say hi, since I've not seen them for a so long time.
What has happened few times is, that someone is asking to accept me to be their friend and I really don't recognise from their name that who is this person. Then the next thing I do is, check mutual friends, and from that list I often realise what is the context I should this person. And often I do accept the invitation. For me, Facebook really isn't that personal.
With my offline life friends we have set our own social network. First it was in Ning, but then they decided to ask money for it, so we change to Grou.ps. I think this excellent setup, then I do have lot more of control with whom I share what. I truely recommend to give Grou.ps a try if you are fed up with facebook privacy changing every month.