ubuntu hangs while shutting down

[Roger]

For me ubuntu has increasing problems.
Hangs on startup sometimes, hangs on shutdown often,
but mostly hangs in use, windows go grey and everything is locked, 
sometimes up to 30 seconds
For some reason it uses all the CPU and memory during these lockups.
Frankly I now use Fedora 16 more often than troublesome ubuntu.
Before the new Unity Ubuntu was rock solid but now?
I think it for us it's the Ubuntu  nvidia driver. My Fedora uses the 
Nouveau driver.
Roger