I've got an ATI product in 2 of my personal systems, plus I've had as many ATI video cards as I've had nVidia video cards. And I didn't start putting together computers last week either. I've used and worked with, and mostly personally owned at least one example of the leading nVidia and ATI product families starting with the TNT (the original) and working your way all the way to the present era. The only generation ATI that I have never personally owned or worked with is the latest x300,x600,etc series stuff. Last I messed around with is Radeon 9700/9800 era stuff.
With that said, I think their drivers are unstable compared to nVidias. There is nothing wrong with the performance of their hardware, I just dislike their drivers, since they have caused me more problems on more systems than I care to remember. Unless they've significantly changed their drivers, which I see no indication of when I update the drivers for my older ATI cards, I simply don't like them.
You can disagree if you want, but don't presume to know my level of experience with ATI and nVidia. I do not "talk before I walk".