There will be two real life advantages in the future to using Vista with Pro Audio.
First is multiprocessor scaling which will allow your multiprocessor (4-8 and above) machine to actually use all of its cores more effeciently than XP currently allows. The direction is going toward more and more cores and this will be a large advantage in the future. Even now I'm setting up 8 core systems which Vista actually will handle better.
Secondly is memory, but only in Vista64. The 3-4GB memory limitation is gone and were looking at 16GB RAM systems and up for the future. What does this mean? Tons of samples, VSTi's, effects. This will be huge for the people running EastWest or Vienna and doing symphonic scoring. This will make Giga even more archaic than it even is today. Plus you'll only need one machine to run all the samples AND do the mix on.
We will be able to do things with one machine which used to require 3,4,5 computers because the hardware will not be as limited by the software. OF COURSE, now the limitation is the Pro Audio manufacturers. They all need to get their butts in gear and develop the hardware and software to take advantage of all this power that is now available. The machine next to me is an Intel Quadcore with 8GB of Ram running Vista64. But I can't really put it through its paces because the audio stuff is behind.
Its not here yet. When things are developed and its ready, it will be excellent.