Over night Arceri completed two of the requirements needed for the ARB_enhanced_layouts extension mandated by OpenGL 4.4. The two bits are forced alignment within blocks and explicit byte offsets for blocks.
ARB_enhanced_layouts still needs specified vec4-slot component numbers and specified transform/feedback layout support before this extension is completed. However, this is notable as it's the last two portions needed and ARB_enhanced_layouts is the last OpenGL extension that needs to be implemented by core Mesa before it should be in GL 4.4 compliance. (Core Mesa also still needs to finish ARB_robust_buffer_access_behavior to finish out its GL 4.3 support.) In other words, core Mesa is getting close to having OpenGL 4.4 support but it could still be some time before the hardware Mesa and Gallium3D drivers are all caught up with their extension coverage.
You can see the latest commits here that are heading into Mesa 11.3-devel.