Open source desktops and closed source video drivers.
When you have a workstation running some variant of Linux, the Gnome desktop and you have an nVidia graphics card in the box, do yourself a favor and install their drivers. Make sure that the "Driver" line in /etc/X11/xorg.conf reads "nvidia" and not "nv". And when you get around to configuring multiple displays on the same system, don't mess with Gnome's System->Preferences->Display utility, use the nvidia-settings utility to do it for you (it'll ask for the root password).