Sleepless in Ottawa

Question

Every few days my Macbook gets into a state where it will not go to sleep or shut down. Doesn't matter how I try to put it to sleep (apple menu, brief press of power button, or close the lid). It just keeps running though if I close the lid it does turn off the backlight.
When it is in that state it also will not shut down. It gets to a plain blue screen with the little line that circles once per second, and stays there forever (well at least for an hour). The only way out is to press and hold the power button to force power down. At least it always boots cleanly afterward, so it must have been nearly shut down.
To me, this looks as if some process is stuck in a tight loop waiting for an event that never happens, and doesn't see the shutdown request. I've tried killing many non-critical processes once it becomes sleepless, in the hope of getting the culprit, but no luck. Must be a low level system thread.
Back when I was running 10.4.8, I found a way to trigger this state reproducibly. All I had to do was put my Mac to sleep while using my Bluetooth mighty mouse, then wake it up with the mouse out of range. It would wake up fine, and work normally, but from then on it would not go to sleep again. By always turning off the mouse before closing the lid, I was able to run for many days without seeing this problem.
That may be a clue, but it is no longer a reliable trigger in 10.4.10 (and yes, I've installed v1.1 combo updater). I am still getting a sleepless state once in a while, but don't know yet what triggers it. Possibly there is some connection with using the Mighty Mouse while running Parallels.
1. Is anyone else having problems with an Intel Mac that won't sleep?
2. If so, have you found any way to trigger the problem reproducibly?
3. Any solution?

Answer 1

Thanks for the suggestions.
All I have to do to get back to normal is reboot (after a forced power down, of course, since restart never completes), and for hours or even days the Macbook will sleep and shutdown normally. Then suddenly some unknown trigger puts it into a sleepless state.
I did try all the resetting and pref trashing options months ago, and they made no difference. I may do it again; it can't do much harm. But that's more likely to help a Mac that will NEVER go to sleep or shut down. I'm 90% sure that this is a software issue related to some low level kernel thread that is not terminating normally because of a deadlock or a faulty check for some expected external event.