I ended up with Vista 32 on my new machine, and it's worked pretty good for me. It runs Max, ZBrush, Carrara, Silo, Hex, Poser, Photoshop, or any of my other software fine.

Personally, I didn't care for Aero, but it's easy to shut off. Same with the "are you sure" nags, though (to be fair) I did end up shutting off 20 or 25 unnecessary services.
4 gig of ram and a 2 gig readyboost brought it to life. It'll open Poser with a 35 gig internal runtime in 12 seconds, which is fast enough for me.
It's been as solid as anything else I've used, so I really can't complain. I would have preferred to wait for a service pack or two, but my new machine had it on it so I just thought I would see how it worked for me.
It does a few things different from XP, but the way I have it set up I can't tell much difference.