This is becoming annoying for me since 10.5.1. For no apparent reason, Shut Down normally happens within 1 - 3 seconds. When this happens the screens are all black lights on the displays but the fans in the tower starts getting faster and faster, louder and louder "wooo 747 take off!". Almost like the sleep problems that are known with Leopard or like OS X has crashed. Only way to solve it is hold the power button down for 5 seconds, then start her up again. Once back into the desktop, Shut Down from the menu, which it cleanly shuts down. It's a totally random issue. Does anyone else suffer this problem with Leopard, when their fans start going crazy after the screens are all off? I never suffered it with the original release of 10.5.