Re: Bug Report: Hard crash (freeze) with nVidia GTX 460
I have faced this kind of problem with a multitude of kernels, NVIDIA driver versions, Xorg versions and cards (and lately even on MacOSX). This has always been related to PowerMizer causing the system to freeze when going from a higher performance level to a lower one. A very easy way to reproduce it is to start a web browser (Firefox or Chrome will do just fine), quickly scroll up/down a page a few times (you can tell when a higher performance profile kicks in because the scrolling suddenly becomes much smoother) then stopping all activity and waiting for the system to crash.
I have always been able to remedy this kind of errors by simply locking PowerMizer to the highest performance level (via nvidia-settings on Linux) OR tricking it to never go back to a lower performance profile (for example by continuously running a movie in VLC in a loop).