Using the 64 bit desktop version of Ubuntu 12.10, macbook pro 7,1 won't shutdown or reboot, it will only go to a blank screen and then hang there forever until the power button is held down for 3 seconds.
As it turns out, the driver for the nvidia graphics card was causing this, however I don't know why. I was using the nvidia-current driver, as the guide here told me to do.
The solution: change the driver the graphics card is using. Software Sources > Additional Drivers > and change the nvidia driver to nvidia-experimental-304
Unable to reboot/shutdown:
Able to reboot/shutdown: