Spent a lot of time with the ati driver today. Got the drm-using ATI driver working in both DMA (CCE/CP) and MMIO modes. Haven't done any benchmarks. It's just a basic conversion of the drivers for r128 and radeon from XFree86 to xserver. It's still lacking, in that the kernel isn't sleeping while waiting for the accelerator to idle, and DMA isn't used for image read/write between card memory and system memory. There are also rough edges (AGP isn't detected yet, and it's probably not working on r200s).
Applied the patch from Michel Daenzer I had worked on for fbdev backend in Xati. It's a little unstable for me when I have fbdev loaded, but I've heard rumors there are issues with radeonfb on 2.6.0-test