Bit of a late resumption but .....
I downloaded the latest Minime2012.08 for a change and it worked well for a time but the same shutdown problem has recurred but worse than before. Whereas it would fail to shudown only occasionally, now it won't shut down at all, neither with gui or terminal. I disabled acpi but that made no difference. I went through all the previously suggested methods including Texstar's replacing .xorg
I get the usual screen verbiage indicating that it is , in fact, powering down, then it hangs tight and I have to turn off the switch on the machine.
Then, when I restart, I find various odd things happening on the screen --- My 6 desktops lose their wallpapers, widgets disappear, or shortcut icons on the desktop and panel change their places.
The only way I can shutdown safely is by resetting the machine and booting Windows XP -- and that is embarrassingly degrading -- I try not to let my wife see what I'm doing.
I have been googling the problem without success. Any help, as always, much appreciated.