For the non-rebranded Sea Islands hardware and then the new Hawaii R9 290 series GPUs there are now patches for enabling 2D tiling, which can be a huge performance win, and MSAA, for anti-aliasing, in the Gallium3D driver.
Found here is a patch by Marek for enabling 2D tiling by default on "CIK" GPUs. This code is contingent upon a new Linux kernel DRM that provides the necessary functionality for CIK 2D tiling.
Found here is a patch changing a few dozen lines of code for handling multi-sample anti-aliasing. Besides needing the new Linux 3.13 kernel DRM, LLVM 3.4 with its AMD GPU back-end is also required for this support.