I don't use Facebook too much. Basically:
1) Easily keep in touch with some of my extended family.
2) Monitor my kids Facebook (yes, I am one of those parents
)
3) Easy discovery point for friends that I have fallen out of touch with, but would very much like to have contact with again.
The legions of people that I have friended, who now bombard me daily with Farmville, Mafia Wars, and other gaming garbage, are pushing me to the edge. I'm almost at the point where I am going to research unfriending people, and send them a message telling them why I did so.
My Facebook is pretty much a sanitized location. Things that are on there would not alarm a potential employer, nor would they shock my parents or in-laws. I do have a link to my LinkedIn page, where my "corporate face" is hosted.