There have been reports about Treos rebooting themselves, and it may have more to do with other things going on in the device than it does with Village Sim. Since the game is only saved when you exit, the safest thing to do is to periodically exit Village Sim and then launch it again. That way you don't lose your progress in the game just because you experienced a reboot, and it doesn't take much time to do it. I typically leave my games running on AC power, too, and it's easy to get engrossed in the game and forget to save it.