Hey,
I tried it. The short answer is that nVIDIA cards are OK for text, but may not work at all under X.
I downloaded the 3.3 ISO's, and burned new CD's. I did an X desktop install on a test bench P3 600 MHz system with a 4.3 gig drive. I did the install with a known-to-work Voodoo Banshee card to get the system going. I used a Mag DX1495 monitor, which I know does not to work on Linux with nVIDIA cards (but which works just fine running Windows with nVIDIA cards).
Everything installed OK with only a minor glitch toward the end (just when going into the reboot, after setting up the monitor and display card, there were some messages about cannot find some graphics files).
After going into my regular user account and adjusting some preferences, I shut the system down, replaced the Voodoo Banshee card with an nVIDIA Riva TNT 2 card, and restarted the computer. During startup, kudzu detected the hardware change, and configured the machine for the new card following my confirmation. (Windows can do this automatically, why not Linux?)
Sure enough, when X tried to load, the screen went blank. Not only did the screen go blank for the X console #7, but the screen was blank for the 6 other consoles as well. I knew this because I could change to my favorite with F2, then Ctl-Alt-del to reboot. The screen stayed blank until the computer began the new boot, when the screen came back.
This was exactly the situation under CentOS 3.1.
Moral of the nVIDIA story: if the monitor/display card/motherboard combination works for you, great. If not, using a display card from a different manufacturer may be the best solution.
IMHO.
Rick