There's patches now floating on the Mesa mailing list that provide support for OpenGL Uniform Buffer Objects (UBOs) in Mesa. This is noteworthy as it's another OpenGL 3.1+ feature that's been sadly missing from this open-source graphics stack.
Published today to the Mesa mailing list
were a set of patches that provide partial support for Uniform Buffer Objects. However, the functionality is not fully complete nor is the driver implementations.
For those curious about Uniform Buffer Object support in OpenGL, see the OpenGL Wiki
for a description and more details.