Did a distro upgrade on Kubuntu to 6.10. Everything was working nicely--firefox 2.0, etc... but I hadn't rebooted yet. My linux box isn't a critical system at work, it's subjected to the whims of the neighborhood power grid. Thus, it had to be turned on after the long weekend. This morning, I discovered that I needed to reinstall the nvidia drivers. The post linked to below contains the details, but if you had the nvidia splash screen prior to 6.10, the line below is probably all you need:
sudo aptitude install linux-generic linux-restricted-modules-`uname -r`
In case there are module difference issues, different display driver versions are available from nVidia here.