When I started my computer the other day, X was not starting. Nothing happened. Just a cold, black screen. I had no idea what triggered this, so I decided to reinstall the NVIDIA driver for my graphics card. All went well and X was working again. After reboot, same problem.
After googling for a while, I found this discussion. Seems the Debian's/Ubuntu's own nvidia runlevel scripts are cleaning up modules they shouldn't. So the solution is to uninstall all nvidia stuf you installed from Debian/Ubuntu (with --purge option), reinstall the NVIDIA driver from the official website and switch to runlevel 2 to see the result.
Aah, don't you just love if everything falls back into place ;)