I'm actually surprised that there hasn't already been more Location Based Service-crime. In addition to stalking, it seems like robbery and theft would be rampant.

There's already been cases where thefts happened after people tweeted that they were going on vacation (http://www.socialreflections.com/twitter-connection-to-home-...). I wouldn't be surprised if the number of social-media related robbery increases as these services continue to gain traction.

By using services that tell people exactly where you are, you're really telling people exactly where you aren't: your home.