While Nexuiz was the worst, the OpenGL performance in other games was choppy at best. Below is a recorded video of Ubuntu 11.04 from this Sandy Bridge setup running the World of Padman game. This illustrates the same problem in all of our tests where the frame-rate is schizophrenic.
The choppy frame-rates also originate with the GPU being hung countless times with the BLT ring idle.
The Intel "Sandy Bridge" experience under Ubuntu 11.04 is certainly better than in Ubuntu 10.10, but it's certainly not pleasant if engaging in anything more than light desktop usage. Kernel mode-setting at least works as does Compiz for enabling the Unity desktop experience, but if pegging the Sandy Bridge processors with a more graphically-demanding workload is where you'll find Natty Narwhal jumped the Sandy Bridge support train.
Besides the core desktop experience, packaged in the Ubuntu 11.04 repository is also only libva 1.0.8 (the latest upstream is v1.0.12), which contains the very early Sandy Bridge decode support for video playback via the VA-API interface. Pushed to the VA-API library repository since then is a fix for VC-1 playback support on Sandy Bridge, shader post-processing support, de-interlacing / scaling, and many other Intel/SNB improvements. In the yet-to-be-released libva 1.0.13 release is also SNB Linux video encoding support.