Comment 4 for bug 98668

I can verify that for me the issue was the deprecated i810 driver. I had upgraded from Feisty (where my laptop didn't suffer this problem) to Gutsy, but because I had manually changed xorg.conf a long while back (for an unrelated issue), Xorg continued to use the i810 driver.

Running:
sudo dpkg-reconfigure -phigh xserver-xorg

to automatically update my xorg.conf (as suggested in the file itself) straightened out my xorg setup and my computer hasn't exhibited the freezing behaviour since.