Primarily performance increases for the newer ATI/AMD GPUs, but more interesting to me is the amount of issues/bugs fixed compared to previous releases.
You can download the new drivers from
here. You can read the release notes
here.
ATI/AMD has really come around in the driver department in the past few years. In the past, NVidia used to be the king for stable drivers, but the opposite is true these days for Vista drivers and to a certain extent, even the newer XP drivers.
Just a few years ago, after being an ATI fanboy since the VGAWonder days, I swore off ever buying another ATI product due to their non-support of older graphics cards and horrible driver bugs. They were always excellent for image quality, normally on par with Matrox, but I had too many problems with the old drivers.
Now, Nvidia and ATI are about 'equal' in my opinion on image quality and Matrox is now a niche-market player only. I used to have systems with multiple Matrox Millennium PCI cards for insane multi-monitor setups. I still have a pile of those cards around somewhere.