As one can see, Intel clearly made some very nice performance improvements between the Linux 3.2 kernel at the beginning of 2012 and now with the Linux 3.6 kernel that's presently under development and will be released in the coming weeks.
This hasn't been all the Intel Open-Source Technology Center developers have been working on, but the Intel Mesa driver has also improved much this year when it comes to the OpenGL performance as well as features and better supporting the more recent OpenGL specifications, with now nearly at OpenGL 3.1 compliance but still having a ways to go to be at OpenGL 4.3.
A majority of the DRM performance boosts came out of the Linux 3.4 kernel upgrade, for those wondering about more details there, see the Phoronix articles on Linux 3.4 Kernel Strengthens Intel Graphics and Sandy Bridge Becomes Quicker With Linux 3.3/3.4 for explanations. And for the Intel DRM Linux 3.5 improvements, see DRM Changes In Linux 3.5 Are Huge.
Stay tuned for the upcoming Intel Sandy Bridge OpenGL comparison under OS X, Windows, and Ubuntu Linux.