I have a 20" aluminum macbook, but I think this is only a Leopard issue right now. Sometimes when I try to restart, shutdown, or logout it will freeze in a number of ways. The first way is to say a program refused to shut down. Even if you close all of them and do it again it waits for time outs and says something else didn't shut down. Keeping trying the different ones and eventually it only shows the background and gets rid of the top menu bar. You can still move the mouse over the dock though. The only way to fix it is to hold the power button down to shut it off. Another time it was almost ready to restart and then it did the circle made of lines it moves in a circle and did that for a long time until I finally held the power button down to shut it off again. Sometimes it works fine and other times it does that. I'm running 10.5.6 with a fresh re-install of the OS only a few weeks ago.