With Ivy Bridge, Haswell, Bay Trail, and now Broadwell stealing all the attention of the Intel Open-Source Technology Center crew, Sandy Bridge is now largely an after thought within the open-source graphics driver. Of OpenGL 3.2 support, the lack of geometry shaders has been the main blocker, but Intel hasn't been proactive about implementing the support. It's possible to implement GS on Sandy Bridge, but it works differently than newer generations of hardware so is a greater commitment to support, and there's talk that it's not even exposed by the Intel Windows driver. As a result, Sandy Bridge has been tapped out at OpenGL 3.1 compliance although the Intel OTC developers said the necessary documentation is out there that any interested independent parties could potentially accomplish geometry shaders for this sixth generation Intel HD Graphics hardware.
Today that milestone has finally been reached with the community picking up the slack. Iago Toral Quiroga and Samuel Iglesias Gonsalvez of Igalia tackled the geometry shader support in Sandy Bridge. This work by the infrequent Mesa contributors implements the necessary support, doesn't expose any new Piglit regressions, and then after landing the support goes ahead to enable GL Shading Language (GLSL 1.5) and OpenGL 3.2 for Sandy Bridge hardware.
This work is spread across 37 Mesa patches but will hopefully be reviewed (and approved) in time for the upcoming Mesa 10.3 release. This great work for now can be found on the Mesa-dev list.