At the end of the day, Facebook's facial recognition technology is downright creepy. Opting out of the service doesn't mean Facebook will stop trying to recognize your face--it just means that Facebook will stop suggesting that other people tag you. Even Google has noted the utter creepiness of facial recognition technology (though I suspect they're just waiting for Facebook to get burned).
Facial recognition technology will ultimately culminate in the ability to search for people using just a picture. And that will be the end of privacy as we know it--imagine, a world in which someone can simply take a photo of you on the street, in a crowd, or with a telephoto lens, and discover everything about you on the internet.
Obviously, we can't stop the world of technology from moving toward the development of accurate facial recognition software. But so far, no facial recognition software has really been a threat to our privacy, because nobody has that huge database of people and photos required. Oh wait, except Facebook totally does.
Yeah. So not only should you opt out of Facebook's facial recognition technology by going to Account > Account Settings > Privacy > Customize Settings > Things Others Share and disabling "Suggest photos of me to friends," you should also upload random pictures of trees and animals and stuffed toys and tag them as yourself.