Grigori Goronzy posted to the mailing list a set of patches for Evergreen/Cayman that reportedly improve the performance of 2D rendering for most workloads. The changes he say are also applicable to R600/R700 hardware.
The optimizations include handling of non-overlapping same-surface copy operations, better solid pixmap support, and acceleration of the PictOpOver operation with a component alpha channel. The improvements mostly benefit workloads using solid pixmaps or where a lot of text is to be rendered.
The 2D AMD Radeon performance optimizations can be found on the mailing list. AMD's Alex Deucher has already reviewed and tested the work so it may be merged into the mainline xf86-video-ati driver soon enough.