I spent a few minutes starting to write a "Why I Deleted My Facebook Account" essay, only to decide that this has been done many times in the last few weeks. Follow the link for a fairly complete rundown.
In a nutshell, in all my internet affairs over the last 20 years i have never been concerned about my personal information being shared in some way without my knowledge. Facebook changed that.
You can still find me on Twitter and elsewhere. My Google profile has other links.
My FB account will be gone by months end.
Update: Please use this tool to be sure your Facebook account privacy settings reflect your expectations of the service.