A few days back I published benchmarks showing Intel's Ivy Bridge hardware regressing with Mesa 8.1. While those problems are still outstanding, the good news is that Intel's previous-generation Sandy Bridge hardware appears unaffected. Overall, Sandy Bridge is performing well with the soon-to-be-released Mesa 8.1 library for open-source Linux graphics drivers.
To see whether Sandy Bridge was affected by the Ivy Bridge regressions on Mesa Git master, from an Intel Core i5 2520M "Sandy Bridge" laptop running Ubuntu 12.10 with Unity 2D and the Linux 3.5 kernel with xf86-video-intel 2.20.2+ and libdrm Git, benchmarks were done of Mesa Git master (8.11-devel) and then the Git branches of 8.0 (8.0.4) and 7.11 (7.11.2).
The Mesa build is the only component being swapped out during this round of testing from a completely different configuration than the recent Ivy Bridge results. All benchmarking was handled via the Phoronix Test Suite.