I've had this problem for a long time, since Hoary I think, but I found a workaround recently. In my case, a kernel-module causes my 'Asus P5GDC Deluxe' not to power off. I don't know which one, though. Tried to blacklist all modules one by one, but gave up after booting over 10 times. Then I wrote a small script that just unloads all modules just before powering off.
I've had this problem for a long time, since Hoary I think, but I found a workaround recently. In my case, a kernel-module causes my 'Asus P5GDC Deluxe' not to power off. I don't know which one, though. Tried to blacklist all modules one by one, but gave up after booting over 10 times. Then I wrote a small script that just unloads all modules just before powering off.
Install:
sudo cp -v /path/to/rmmod-all /etc/init.d/
cd /etc/rc0.d
sudo ln -s ../init.d/rmmod-all S89rmmod-all
Remove: d/rmmod- all /etc/rc0. d/S89rmmod- all
sudo rm /etc/init.