Brian Paul has merged his draw-instanced branch, which adds GL_ARB_draw_instanced and GL_ARB_instanced_arrays support. Instanced drawing was inroduced as part of GLSL 1.30 and now allows GL3.txt to be updated. This support is available to Gallium3D drivers via the Mesa state tracker.
As far as OpenGL 3.0 support in Mesa is concerned, still left to be tackled is some GL Shading Language functionality, GL_EXT_texture_compression_rgtc, and sRGB frame-buffer support. There is also a few started but uncompleted tasks like float textures and render buffers, non-normalized Integer formats, and transform feedback. Then for OpenGL 3.1, 3.2, and 3.3 there still is much more work to be done. That's even before getting to OpenGL 4.0 support, which is completely unsupported in Mesa at this point. The full OpenGL 3/4 state file as of right now can be found via CGit.
Meanwhile, David Airlie added support to Mesa for GL_EXT_texture_sRGB_decode. This is a very new OpenGL extension that isn't even at version 1.0 as far as its specification goes and its latest revision is dated from just 18 November of last year. The GL_EXT_texture_sRGB_decode extension created by Apple can be read at Khronos.org. The GL_EXT_texture_sRGB_decode support is currently available to Gallium3D drivers, the Mesa software rasterizer, and the Intel i965 classic driver.
Last but not least, Brian also added support for the GL_ARB_draw_buffers_blend extension to Mesa and it's currently supported by the Gallium3D drivers.
This work, plus improvements going into the various Gallium3D and classic Mesa drivers along with state trackers, etc will eventually be released as Mesa 7.11 in a few months time.