This was the system used for delivering the Intel Sandy Bridge Linux results.
First of all, when adjusting the engine visual quality settings of low, high, and ultra, there wasn't much in the way to note of visual differences as rendered by the current Intel Mesa driver. The frame-rate when running the well-known "demo1" benchmark from the Phoronix Test Suite also did not change much regardless of the three image quality settings tested. Those settings were tested at a variety of resolutions.
In terms of how well the open-source Mesa driver performed, at 800 x 600 the Sandy Bridge (HD 3000) graphics were pushing out an average of 43 FPS, dropped to 32 FPS at 1024 x 768, 21 FPS at 1280 x 1024, and 15 FPS at 1920 x 1080. Even with this latest-generation of Intel HD graphics and the very latest Linux driver code, the Doom 3 experience is not really acceptable for gamers due to the frequent problems and overall slow performance.
Within Mesa/Gallium3D we will hopefully see S3TC support finally (in a legal manner) landing soon. Intel's Linux developers believe the S3TC patent is invalid and more recently, HTC (the owner of S3 Graphics) joined the Open Invention Network.