What do you share?

I have a handful of people that I really consider to be my "friends" on Facebook. There are countless numbers of people that I could contact as ask to acknowledge knowing me on Facebook ... but I don't do this. I really think it is pointless to have 400 people in my circle of friends and fail to understand why people do this. Do you really think anyone believes that you are truly friends with that many people? I further question why people would want to share information about themselves on a daily basis with that many people? It just seems like a good way to invite problems. If you have scads of friends on Facebook just how much do you really share about yourself?