My Dell has an nvidia card. I run Gutsy. At work I have a 24" widescreen (Acer AL2416W) to plug into my laptop to use as a primary screen, so I have more screen real estate to work with.
It took me a couple of hours to arrive at a workable solution.
Note to self for future reference: DO NOT USE displayconfig-gtk. It doesn't know what the work monitor is, and throws errors when trying to use mirror mode.
DO use nvidia-settings. This is part of nvidia-glx-new. However, backing up the xorg.conf file first is a remarkably good idea.
At present, I don't know of a good way to set up xorg.conf profiles, I guess, depending on whether or not I'm at work. Any ideas, lazyweb?