What I was talking is that unfortunately (and that doesn't just apply to AMD/ATI cards, but also sometimes to nVidia and Intel ones), some hardware (mainly the motherboard chipset used) and software configurations (for instance, your Linux distro / kernel / Xorg Server version combo) can do significant changes in the way your graphics card work... And it's a bit annoying that unfortunately, there are some problems with some hardware/software combinations that aren't easy to solve...
2. I also don't have almost any problems with my ATI cards too (except I've to use Catalyst 10.7 + Xorg 1.8.2 for my HD2600 to properly work with H264 videos)... Otherwise, everything's working fine.
Every card needs powersave, especially high end ones. Without they would need much more power than needed. But thats the price you want to pay for using oss drivers