I had a thought on another brainstorm about using bluetooth status for some actions. For example if the device is paired with my car headset and a friend texts I'd like it to send a message to them saying if it's urgent please give me a call, I can't look at messages right now. It could also set the presence status of any IM clients running to say I'm in the car/not available/whatever.

Also if I'm sitting near my laptop with it turned on I might want the phone to behave differently than if I'm watching my media PC (which has bluetooth).

Somone had mentioned locale too, from android, which has a really interesting plugin set up to allow you to do almost anything when certain location based conditions are active. The granularity of location info can be wifi/call tower/GPS or whatever. I can see a lot of stuff being useful off just cell tower info for me. The GPS is such a battery hog I'd be reluctant to use it for many things.