Ati drivers STILL royally sucks. Catalyst control center looked like a 5 year old designed it with a box of 8 color crayons.
Aside from that; Ati drivers tend to 'not play well' with systems. I've been doing corporate IT (in a CAD environment) for a long.. long.. time, and have seen WAY too many systems end up borked from botched driver updates and etc.
On a clean install they work fine, but all too often ~6 months after the format you install an updated... audio, or network driver which somehow screws up the Ati drivers, which means trying to roll it back or worse - re-image/format. Nvidia drivers just work.. I've never had them mess up an install or update improperly.
That's my .02 unrelated to the topic, lol..