While setting up a test box I came across this issue. The shutdown process hangs and waits.
These steps worked for me http://askubuntu.com/a/123287
Edit the grub config
sudo nano /etc/default/grub
Add acpi=force to this line
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi=force"
Save and update the grub config.
sudo update-grub



