My 2 cents. If you have the hardware go Vista. Most people who complain about Vista have rubbish hardware (usually budget laptops).
I run all games on Vista (COD4, Crysis, CoH, Assassins Creed, COD2 and so on) with NO PROBLEMS. If you have the hardware go for Vista. BTW, Vista's new graphics driver means that aero etc has NO IMPACT on 3D gaming performance. SP1 has made my games much more responsive, and Direct X 10 is the future. You can always dual boot too.
However, it is true to say, at the moment, if you look solely at FPS, XP is faster for gaming. I do think though, that you would be hard pushed to actually notice, although you will be able to notice Direct X 10 soon enough.
Also, don't forget that all of FutureMark's new/future products (e.g. 3DMarkVantage and PCMarkVantage) are/will be Vista only. You will see this trend more often in the future. Another thing, those old enough to remember, will remember that XP was also a pig when it was first released, Vista will mature too.
Just make sure you have adequete hardware.