Keith Whitwell has gone ahead today and merged the softpipe-opt branch of Mesa into the master Mesa branch, which will eventually work its way into Mesa 7.7. The softpipe-opt branch brings performance optimizations to the "softpipe" driver of Gallium3D. The softpipe driver is a pure software implementation of Gallium3D for use in testing and for where a hardware driver has not implemented full support. With the merging of this optimized driver, the performance should be comparable to that of the Mesa Software Rasterizer with the traditional OpenGL stack.
While the performance of the Mesa Software Rasterizer is far from ideal for an end-user as it's just eating up the CPU, more performance optimizations are going into llvmpipe, which uses the Low-Level Virtual Machine for providing some process optimizations. The softpipe driver will remain an area that's used for experimenting with new ideas by developers.
Keith's softpipe-opt merge announcement was made on the mesa3d-dev mailing list