The finest example of social media mining that I have found to-date is the superb site Please Robe Me.
In case you can't guess, it mines the twitter stream in realtime to republish anyone who is telling the world that they are not at home. Who would want to know this? Take a guess.
Check out my new site I'm-bored-and-broke-so-who-can-I-rob?.com. We feature full integration with Google Maps and their latest realtime street stealview technologyTM© - so you can watch your place being robbed as it happens via our iPhone app (a bargain at $599)!