"Vista is the better Windows, because it behaves better, because it looks better and because it feels better. But it cannot perform better than Windows XP. Is this a K.O. for Windows Vista in the enthusiast space?"
If you go to the link, you'll notice in UT 2004, frame rates droped 32.4% while it was running in Vista.
And in F.E.A.R they dropped 8.3%
If you're a gamer, it seems that it's best to hold off on upgrading to Windows Vista until DX10 games are released.
Now it is a good idea to keep in mind that this is with current top of the line hardware. I'm sure we'll see better performance in games as hardware advances.