Even though I've had the same setting (monitor goes to sleep after 10mins) since I got my ALUM MBP 18 months ago, the monitor will often not sleep. It just stays on. I restart...sometimes it will sleep (after appropriate inactivity) and sometimes it won't. I don't have a screen saver of any sort enabled...just monitor goes off at 10 mins. And yes I'm positive the mouse isn't being moved or keys pressed. Ideas?