Three AMD employees have been working on this R600/700 3D support in the DDX, DRM, and Mesa, and now they finally have glxgears running atop their 3D driver that is now based off of the radeon-rewrite driver. There's still a lot of work to be accomplished when it comes to usable open-source 3D support with the ATI R600/700 GPUs, but this is an important step.
More on this milestone is shared on Alex Deucher's blog. In order to experience this GPU-accelerated glxgears with a Radeon HD 2000/3000/4000 series graphics card, the latest xf86-video-ati or xf86-video-radeonhd driver is needed, a special branch of Mesa, and a special branch from the DRM tree. Hopefully within a few weeks/months we will start seeing this OpenGL support work with Compiz and Mesa-supportive games.