Wow, surprised to hear all the nVidia driver hate, I have similar experiences with ATi drivers. I guess your mileage really does vary.
I haven't had any stability problems with the ATI drivers, but I am using an older version of the catalyst drivers on purpose -- The gamma correction screens on the newer ones are too messy... (The newer versions allow you to specify gamma for red/green/blue seperately, but I haven't seen a way to lock them together -- so unless you can get the curves to allign just right, you can easily get weird colors with the newer drivers.