Face book announced that it will soon start automatically suggesting your name for tagging photos any time it thinks it recognizes you in a picture. This automatic facial recognition is the default and will be done unless you explicitly opt out.
It looks like you need to customize your privacy settings to disable this. In Facebook, look under the "account" menu and select "Privacy Settings".
From there click the "Customize settings" link at the bottom of the table. Within there, look for "Suggest photos of me to friends", and set it to "Disabled".
I suspect that few people will simply stumble on that.
Other people tagging you in photos can lead to embarrassment you might want to avoid. Having your name suggested just makes that more likely.
While you are at it, you might want to change the setting that allows others to "check you in" to locations. That can tell thieves you are away from home or stalkers where to find you.
CNN has a good article on the announcement. Facebook lets users opt out of facial recognition - CNN.com