In VTK 6.1 features (such as FBO) that have been disabled for OSMesa because of driver bugs in previous versions have been tested against the latest releases of Mesa. Most of the algorithms can be used with the latest Mesa release (9.2.2). In Mesa release 9.2.0, OSMesa can be provided by the Gallium llvmpipe renderer. The llvmpipe renderer has threading (currently only for fragment shaders) and uses LLVM for JIT compilation of GLSL shaders.
Gallium llvmpipe benchmarks
The following chart shows the run time of VTK's Rendering ctests with OSMesa classic, Gallium llvmpipe OSMesa state-tracker, and an ATI Radeon HD 7870.