Thanks Robert, I've done a clean install of Ubuntu 13.04 64 bit and
performed something like 30 shut down and restarts. I was delighted to
see that there was no hanging on shutdowns or restarts at all - not even
once!
Along the way, I tried the default Nouveau driver, and the nvidia-310
and -313 d
I also think there are posts for different problems pointing at this
bug. I followed one of them here and added my name to the list. But now
I too am not sure of this and have removed myself as being affected by
it.
Here are my experiences, in case they help. I have a Core 2 Duo desktop
and a GeFo