Uniform Buffer Objects is a feature of OpenGL 3.1 and is a buffer object storing uniform data for a shader program. [Those interested in details about OpenGL UBO can find more information on the OpenGL.org Wiki.]
Back during Oktoberfest there was the original UBO patch-set for Mesa, but Vincent has now cleaned up the patches and made a few other changes. This updated version of the Uniform Buffer Object patch-set is now a set of 17 patches against Mesa Git master.
Details on this latest patch-set for the GL_ARB_uniform_buffer_object extension and related work can be found beginning with this mailing list message.
Still to be worked on is i965 DRI driver support along with UBO Gallium3D support for the LLVMpipe, R600g, and vmwgfx graphics drivers. There also needs to be matrix support at code generation, API queries for classic uniform, support for shared and packed layouts, and other technical items to address.
As Mesa 8.0 will be branched from Git master soon, it's unknown whether these remaining changes will land in time to make it into this next Mesa release or if it will be another six months before seeing UBO in a new release (Mesa 8.1).
At least I'm not the only one doing work on Christmas in the Linux world...