A twitter client. No, really. There's only a small handful of native Mac twitter clients, compared to the plethora of iOS clients. And I believe that @ev recently said that Tweetie|Mac isn't going to get updated anytime soon.

Or a small app that only runs in the menubar that will disable or enable bluetooth whenever I hit a key combo. Or when I move into or out of a certain location (Core Location exists on 10.6). Maybe if the person's on a laptop and they disconnect from a power source, turn it off, etc.