Novell's Matthias Hopf has mentioned that this register documentation is in excess of 650 pages... It's much larger than the R500 3D programming documentation released earlier this year due to the plethora of architectural changes. In addition to this pending R600 3D documentation dump, the release of the "TCore" source-code is imminent, which will also help in setting up the R600 2D/3D support.
Matthias Hopf has brought up the R600 DRM (or there the current lack of) on the DRI mailing list. He's going to begin tackling the R600 DRM (Direct Rendering Manager) implementation and hopes that the R600 series -- like the R500 3D support -- can initially function as an extension of the Radeon driver. Later on the code may be broken up to better support some X features (such as DRI2) and varying hardware features between the different ATI product generations.