OK, I just got the 31 kernel from git, with the latest drm-next bits, as described in the build howto. I also got the latest mesa, ati-radeon and libdrm from git. I observe the same thing that I did with the 32.rc1 kernel.
This is KMS/DRI2. KDE effects work, as does neverball. Things work(ed) fine with DRI1/non-KMS.
openarena: radeon_cs_gem.c:121: cs_gem_write_reloc: Assertion `bo->space_accounted' failed. .... drmRadeonCmdBuffer: -22. Kernel failed to parse or rejected command stream. See dmesg for more info.
[ 128.157945] [drm:r600_cs_packet_parse] *ERROR* Can not parse packet at 548 after CS end 548 ! [ 128.157948] [drm:r600_packet3_check] *ERROR* bad DRAW_INDEX [ 128.157950] [drm:radeon_cs_ioctl] *ERROR* Invalid command stream !