To be quite honest, I've had absolutely NOTHING but trouble using ATI cards in the past. I've bought 3, and I've had 3 die on me, or simply not work at all. For one of them I was able to get it to work by using Omega drivers (ATI's drivers crashed my machine endlessly, and I'm simply assuming it was their drivers because as soon as I uninstalled them, it never crashed again).
My personal preference will still continue to be nVidia, because I've never had a problem with them on vista yet. I continue to get 50-60 FPS on any game I play, regardless of settings usually.
To answer the original point, however: I didn't notice a difference in these drivers from the last ones. From a performance standpoint, that is.
Never overclock your system. Never buy cheap video cards and overclock them. Never buy cards with passive cooling.
Simple rules. I never had any problems with ATI cards.
Have a gigabyte 7600 GT with passive cooling; it works just fine, including at full load; It even overclocks without issue (although I don't personally, just tried it to see).. So I don't know about that. Moreover, it sits at 50c-60c.
While those "simple rules" might have some amount of truth in them, they are simply vague guidelines, and what it comes down to is research what you buy and make an informed decision.
For me that means staying the hell away from ATI, with their awful driver quality (XP, linux - don't know about vista), and having 3 of the damn cards die on me over the years. NV has never given me issues, but it seems different for everyone; Either they have tons of issues with nvidia, or tons of issues with ATI.