When I turn off my Magic Mouse for an extended period of time (I don't know, 30 minutes+), it seems to forget my connection with the mouse and I have to reestablish it through the system preferences. I also have the Apple Wireless Keyboard, but that always connects no matter how long it has been turned off. It's not a big deal. It's just annoying that I have to go into the settings all the time. Thanks - any help would be useful.
So I'm #48. I'd delete your mouse from Bluetooth in System Preferences, then get it discovered again.
This actually should have been in the "Mac Hardware" section. Thats probably why you didn't get a response right away. Second- I believe the previous poster is correct. Delete the profile for the Magic Mouse then reconnect it.