I have the same problem with Debian wheezy(gnome 3), this is why I come to ubuntu 12.04. Unfortunately ubuntu has the problem too. But Debian wheezy with xfce desktop environment can shutting down normally with a warn message sometimes: killing all remaining processes failed.
I have the same problem with Debian wheezy(gnome 3), this is why I come to ubuntu 12.04. Unfortunately ubuntu has the problem too. But Debian wheezy with xfce desktop environment can shutting down normally with a warn message sometimes: killing all remaining processes failed.