Being "friends" with my manager has definitely made me think twice about what I post. Then again, I never posted anything as bad as this about my work:
http://tastybooze.com/2009/08/facebook-fail/ 
Also, I friended my big whom I had lost touch with. She accepted. Then, a couple of months later, I saw that facebook was suggesting that I become friends with her. I always wondered why she defriended me. A few weeks ago, she sent me a friend request. Seems kind of bipolar to me.