The ATI R600/700 3D driver is derived from the Radeon driver rewrite and is currently living in a branch off of Mesa. DRM code that is also not living in the mainline code-base is also required for any level of 3D support. Bridgman shares on his blog that now approximately 25% of their test cases are passing, but the remaining majority are either crashing or rendering incorrectly.
With not even yet reaching the glxgears milestone, this 3D driver is currently not too useful for owners of the ATI Radeon HD 2000/3000/4000 series hardware. However, hopefully by the end of summer it will in good standing and usable.