Chris Wilson has published a new patch series for using LLC cache on Sandy Bridge / "Gen 6" graphics. The LLC work was started by Eric Anholt, but Chris Wilson has continued on with various Intel SNB improvements.
As far as what the LLC caching on Sandy Bridge CPUs means for graphics performance, the Sandy Bridge graphics performance goes up by an additional 10% with the OpenArena game, for example.
This provided a 10.4% +/- 1.5% (n=3) performance improvement on openarena on my laptop. We have more room to improve with doing LLC caching for display using GFDT, and in doing LLC+MLC caching, but this was an easy performance win and incremental improvement toward those two.
The patch-set is currently sitting on the Intel-gfx mailing list. Though unless this is pushed into the DRM tree in the next few days, it's unlikely it will land prior to the Linux 2.6.40 kernel. The Linux 2.6.39 kernel is already looking to be quite interesting without this work, in particular due to major Nouveau performance wins, but this set of 15 patches to the Intel DRM driver will probably not land there. Hitting 2.6.39 wouldn't mean much for most Linux desktop users anyways since Ubuntu 11.04 and Fedora 15 are already set to ship with the Linux 2.6.38 kernel.