Such a touchy subject... Maybe I too have too many skeletons in my closet - I can't tell you how many old people I so hoped to forget found me on MySpace before they started allowing people to go "Private".
I actually recently moved to FaceBook - but only family and extremely close friends. The "coworkers" who you are friendly with but really don't want knowing your personal business just get ignored. I learned that from MySpace when people in my company had way too much information about my personal life - because another coworker who I was "friends" with was reporting back to them... it got completely out of hand. I finally had enough and removed everyone I wouldn't share my life secrets with...
Then I got married and had a kid, and just stopped caring about the "social networking". I'm more about "family networking" - as in, come home, and enjoy time with my family... screw the online sites other than the most basic communication.
The only advantage FB has right now is that my sisters both post pictures of the family on there to share with their close friends and family - so it gives me a way to see my nieces and nephews - that part I do enjoy immensely, since it's not like I can make it to PA all that often...