An interesting article in the New Scientist should cause concerns if you're worried about your privacy. Their engineers have been testing a new algorithm to identify people - not based on their facial features - but on how they dress, pose, their hair and so on. They took 40,000 pictures from Flickr and were able to recognise people with 83% accuracy, even when the faces weren't available. That's equally impressive and scary at the same time.
Two sides to this coin - if Facebook can do it, so can anyone else. Which means that your ability to remain private in today's world is becoming harder and harder. If a friend or colleague tags you in a picture on a service (wouldn't necessarily have to be Facebook, if we're assuming this software gains wider use) then you're potentially going to be found in a lot of different places. Once you start to pull in content from Instagram or other photograph sharing websites which are giving instant access to images, it's at least in theory going to be possible to track someone who is say, doing the tourist thing. Once you know where someone is, and what they're doing, it's at least possible to work out where they're going to be next.
The other side of the coin is that you could equally have software that alerts you when a photograph of you appears on the net - in the background of another image for example. I'm not sure that there's much you could actually then do about that, but at least you'd be in a position to know.