there has been a lot of "freezing" situations so just be clear:
You can not move the mouse or use buttons on the keyboard (like Alt + F)
and even after waiting say 10 minutes - the computer is still frozen.

If you can move the mouse around then you have a slightly different issue.

As for total freezing - if you are on 10.04 you can either move on to
10.10 or back to 9.10.