Comment 26 for bug 566324

Finally seem to have made progress on this.

First thing I tried was upgrade to to the Maverick kernel (2.6.35-20).
That did not fix it, but I was now getting a "Ubuntu is running in low graphics..." message when the crash
happened instead of the black screen.

I was able to avoid a crash by clicking on cancel, getting back to the desktop.

As I was now able to work around the problem, I noticed that playing sudoku appeared to cause it quite reliably.
From reading the bug #541492 description & from Ubuntu forums, I tried the following:-

sudo add-apt-repository ppa:glasen/intel-driver
sudo apt-get update && sudo apt-get upgrade
sudo reboot
sudo add-apt-repository ppa:glasen/855gm-fix
sudo apt-get update && sudo apt-get install dkms 855gm-fix-exp-dkms

Now the system is stable, no crashes since, no matter how much suduku I play.