Originally Posted By: DWallach
I have similar issues with my Mac Pro at home. No Bluetooth at all, but even though I've set it to go to sleep on its own, it doesn't. I set an additional timer for it to go to sleep every morning at 9am, and that seems to help as well, but there will be says I come home from work and it's on.

If you open the Console.app, and switch to all messages, the kernel will log reasons for sleep and wake. If you manually put it to sleep, and it wakes back up on it's own, the log may help narrow down why. It could be a particular device attached, or it could be Wake on Demand related if "Wake on network access" is checked in the Power system preference. I've had a few cases where I didn't disconnect a file share to the Mac Pro, and a work computer was constantly waking the system back up.