Vista 32-bit bad. Vista 64-bit good. Not sure about WIndows 7 yet.
I have extensively used MS Windows products since MS OS/2 was released. I find every version ( with the exception of Windows ME, that was a sad excuse for a new OS ) is on average better than the one before after SP1 has been released. However with Vista I have run in to something odd. Vista 32-bit runs well enough but I find is not stable in the long run. Vista 64-bit is not only faster than 32-bit, but is also much more stable. Playing with the Windows 7 betas I am finding the same thing more or less. With 64-bit drivers almost as available as 32-bit drivers now I am moving my systems all to 64-bit and am enjoying the speed boost and stability.