Facebook has launched their own location-based check-in service called Places, and updated their iPhone app to support it, but will you be using it?
Some people maintain sharing your life, and your location, allows for "serendipitous" discovery -- people who you may never otherwise know or meet see you're nearby and take the opportunity to say hello. Others think it's pretty much a gateway to everything from embarrassment to stalking.
What makes Facebook a little different is that even your friends can check you into Places, unless you turn them down or turn it off.
Who are you comfortable sharing your Places/location with? No one? Just friends? Friends of friends? Everyone?