Vista actually sees the first implementation of our new OpenGL driver, so there has been much work put into it. Yes, there is improvements to be made, and you'll be seeing more performance increases under OpenGL In Vista Catalyst 7.2:While it's very clear AMD(ATi) D3D driver(s) in Vista have had more work put into them, it's certainly not clear that their OpenGL drivers have had the same treatment.
http://www.pcper.com/article.php?aid=367
[Edit] That article also has some interesting stats on our downloads, that gives some insight as to the Vista adoption rate and x64 adoption (at least, among ATI Radeon graphics user community).