Mirkin spent his Saturday evening sending out shader image patches for the Mesa state tracker. This work is for exposing the ARB_shader_image_load_store, ARB_shader_image_size extensions, and the image component of ARB_shader_texture_image_samples.
Before getting too excited, while the state tracker code is now wired up there is not any driver implementing the required parts yet, meaning for end-users this shader image support isn't ready yet. Mirkin has been working on the Nouveau NVC0 support, but it isn't ready yet, nevertheless it's a step forward in the direction of Nouveau's ongoing compute support work. Hopefully we will see Radeon and Nouveau fully supporting this work by Mesa 11.2 release time.
If you are unfamiliar with the shader image work, see the OpenGL.org Wiki and the specification for ARB_shader_image_load_store. ARB_shader_image_load_store is needed for OpenGL 4.2 compliance and ARB_shader_image_size is needed for OpenGL 4.3. Both of these extensions are also needed for OpenGL ES 3.1 compliance. The Intel Mesa driver already has exposed ARB_shader_image_load_store.
Once this work lands along with the NVC0 implementation, Nouveau for GeForce GTX 400 "Fermi" GPUs and newer will have OpenGL 4.2 compliance!