Here's the commit that adds in the hardware context support patch, which is for the i965 classic hardware driver and this feature covers from "Gen4" up through the latest Sandy/Ivy Bridge graphics processors as well as the next-generation Haswell and Valley View processors.
Intel's been working on hardware context support patches going back to February. As already talked about, the hardware context support allows for the graphics processor to save and restore certain state between batch-buffers rather than needing to re-emit the entire state each time. This is one of the requirements for providing OpenGL transform feedback.
The Intel hardware context support work also requires a new libdrm and Linux kernel. Now required to build the Intel Mesa driver is libdrm 2.4.37 rather than libdrm 2.4.34. If wishing to take advantage of the support, the Linux 3.4 kernel or newer must also be used.
Then on the Radeon side, Vadim Girlin's improve flushed depth texture handling path was merged. This is the patch that Vadim claims allows for a ~30% performance boost in Lightsmark and other OpenGL workloads when flushed depth textures are frequently used. For more information on that work, see A New Patch To Improve Radeon Gallium3D Performance.
As already covered, Marek Olšák filed 22 patches of other Radeon / Gallium3D improvements too.
All of this work will be part of Mesa 8.1, which is slated for release in August.