Yesterday Facebook rolled out a new feature called Places that lets you and your friends check in to locations, Foursquare-style. If you'd prefer to keep your location private, or at least stop your friends from posting it, here's how.
You're on the internet reading this post, so it's safe to assume you use FaceBook. Seriously, who doesn't nowadays? Shutins and paranoid schizophrenics?
(So.....I have my offensive comment of the day made, now.)
My point is, unless you are a Foursquare or Gowalla devotee, you probably aren't interested in your friends knowing where you are at all times. Follow the link to learn how to change your Facebook Places settings.