1. Based on what I've seen/heard at a number of different sites (including commments here), ATI's Open GL Drivers are supposed to be crap. Hopefully, these benchmarks will give ATI a good reason to work on the Open GL side of drivers instead of focusing purely on the Direct 3D side.
2. I expect ATI's future drivers to see significantly bigger performance increases in Doom 3 than future drivers from nvidia. This is because ATI can most likely claim a significant increase in Doom 3 performance just by improving their Open GL drivers to the point where they are more on par with the quality of nvidia's drivers (i.e. ATI needs to make their Open GL drivers as good as their Direct 3D drivers are).
3. You need a 512MB+ card to run in Ultra Quality according to id. This means no matter what card you buy now, you'll still be buying nvidia/ati's latest $600 video card 6 months from now if you have to run Doom 3 at the highest settings possible.
4. "Doom 3 has settings that will make the game look even better on hardware that doesn't exist yet (beyond just upping the resolution, like in most games)." - quote from Robert Duffy, lead programmer, id software in the sept 2004 issue of PC Gamer.
Yeah, I'm definitely waiting before I run out and buy a new card (of course I've got a Radeon 9800Pro, so it's not like I'm stuck with a GF MX).