Having Radeons as the most popular videocards around you can't tell me you didn't see it coming. We have finally posted our ATI Radeon 9x00 tweaking guide
that will give you a hand optimizing your system for best compatibility & performance.
You can read the full guide here
, first page goes through basic troubleshooting steps and general settings, then onto more specific Direct3D & OpenGL setting tweaks, performance comparison (benchmarks) between settings and image quality shots to compare different settings results.