Craigslist has had its share of issues with people getting robbed. I don't necessarily think that Craigslist is a bad thing though.
You have the same issue with valets. You give them your keys (which probably contain the keys to your house/apartment), your insurance information is in the glove compartment (which contains your address), and they know that you're not at home because you still need to get your car out of valet.
* http://abcnews.go.com/US/story?id=5930862&page=1
* http://archives.chicagotribune.com/2009/nov/21/news/chi-crai...
* http://articles.latimes.com/2008/jan/11/business/fi-craigsli...
It's the opposite of what was talked about above. They aren't using Craigslist to figure out when people won't be home, they are using it to lure people to a particular place to rob them (and make sure that they will have cash on them).
If any of those location-based services was as big as twitter, I'd fully expect some crime.
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.