The developers working on Mesa within Intel's Open-Source Technology Center have been making steady progress on reaching this OpenGL 3.0 goal in Mesa. The OpenGL 3.0 specification is nearly three years old, but the Mesa/Gallium3D support has lagged behind as invasive infrastructure changes have had to be made, significant GL Shading Language (GLSL) updates, and other changes made. The latest upstream OpenGL specification meanwhile is OpenGL 4.2.
In terms of Mesa hitting OpenGL 3.0 compliance for at least the Intel DRI driver, they are getting very close. Last month the Intel driver managed GLSL 1.30 compliance for "Sandy Bridge" graphics as needed by GL3. Besides the GL Shading Language requirement, in recent weeks they have tackled other OpenGL 3.0 requirements too, but there's still measurable work left to be completed.
OpenGL 3.0 work that's newly published this week are vertex shader texturing support (mail), ARB_depth_buffer_float handling (mail), transform feedback (mail), and prep work for GLX_ARB_create_context support (mail). There's also been various other changes to Mesa in recent days. In regards to most of this Intel OpenGL 3.0 work, it's all focused on Sandy Bridge and future Ivy Bridge graphics hardware.
In terms of what's left, that's reflected by the DRI WorkQueue Wiki page. High priority OpenGL 3.0 action items for Intel that are still outstanding include implementing pass-through GS shader programs, rasterizer discard, verifying the buffer overflow behavior, implementing PRIMITIVES_GENERATED and TRANSFORM_FEEDBACK_PRIMITIVES_WRITTEN queries, a kernel interface for setting rregisters, correct pointer updates on begin/end/pause/resume, and various other items. There's also a fair amount of testing and verification work needed to ensure the OpenGL 3.0 support actually works and is reliable. Plus there's many medium and lower priority work items too.
Within the Mesa Git tree is also the OpenGL status documentation that provides a more concise overview of the support level. What's left to be completed in GL3.txt is non-normalized integer texture/frame-buffer formats, transform feedback (GL_EXT_transform_feedback extension), depth format cube textures, and GLX_ARB_create_context.
Mesa 7.12 is set to be branched from Git master in January, but if the GL3.0 goal is near, Intel's Ian Romanick has mentioned the possibility of slightly delaying this next release. If the support is ready, it will be released as Mesa 8.0.