> (1) Doesn't running the GPS all the time kill battery performance?

I don't think it would need to run all the time, though. Something like polling once every ten minutes, checking more often if the position is actually changing, throttled down to e.g. once an hour if it's in the same place as the last two polls, might be enough. Perhaps existing data could also help here, such as noticing if the cell phone towers used have changed recently. (I really should learn more about how those things work...)

  (2) Isn't this application a bit of a stupid pet trick? Turning the ringer off in theaters?

Hey, I'm not going to complain if it becomes popular.

In addition, I assume Android has the (old) sexy that is accelerometers. So sitting at your desk or only walking a bit might not trigger it.