In Matthias Hopf's blog post he has stated that they are getting close and there's just very few registers they now don't understand. Though they have reached a fully stable programming model for the R600 (Radeon HD 2000 / 3000 series) and RV770 (Radeon HD 4800 series), but the newest graphics cards like the Radeon HD 4550 and Radeon HD 4670 don't yet have this support.
Only basic functionality is supported right now by this code, but that does include textures and shaders. While it's taken this long to get where they are with the R600 2D/3D support and the public has yet to see any code or documentation, Matthias describes the programming as "quite beautiful" for these newer GPUs.
With the ATI R500 series the first bits of open-source 3D support came in March with hardware-accelerated glxgears. Then in May we declared the R500 3D support as a success and it was already running games.
The R600 3D documentation has yet to be released due to legal troubles and such, but at least we have mode-setting support. Back in June the first bits of the R600 Direct Rendering Manager code was pushed out publicly, but with limited use to end-users.
In late August, internally at AMD they had their first hardware-accelerated GL triangles on the RV770 GPU using the open-source stack. AMD's Alex Deucher was foregoing XDS 2008 at the Edinburgh Zoo with the celebrating to prepare this RV770 code for release, but unfortunately this code still has yet to surface.
Though by the looks of it, once this R600/700 code is released, it will hopefully be in a pretty usable state to end-users. Perhaps a nice Christmas gift from AMD?