Comment 2 for bug 114365

Same exact problem. I've been trying to narrow it down. I removed Flash 9, thinking it might be that but it still happens. Running Opera 9, Nvidia proprietary drivers, gaim, and apache2. I've been trying to narrow down the problem this week.
Using USB Logitech G5 mouse with mouse polling set to 2. USB Creative Fata1ty keyboard.

Athlon 64 3600+ X2 Brisbane, Biostar T-Force 550, 2GB G.Skill DDR2 800 :: Feisty Fawn 64

A similar problem related to this I am having is that my active window will stop responding (gnome) and I cannot interact with the screen AT ALL until I press alt+tab. When I do that the Alt+Tab screen flashes for a split second and the system it back to normal. I suspect these two problems are related.

I'll try to use https://help.ubuntu.com/community/DebuggingSystemCrash when it happens again.