Just a quick link, as this is another rather cool little use for a bluetooth connection, beyond mere file transfers.

This link is Ubuntu centered, but it should also work for other distros.

Basically, by pairing your BB with your PC, and running blueproximity, you can do all sorts of rather neat things, from automatically locking your PC once the bluetooth signal strenght drops past a set level and unlocking it once the signal is strong eonugh again, to pausing/re-starting any other running task (via scripts,) that you might want to stop when away from your PC. Think music & video, "away" IM status notifications, etc...