While Ironlake (Clarkdale/Arrandale) -- the generation of Intel hardware prior to Sandy Bridge -- was designed during the OpenGL 2.1 days, much of the OpenGL 3.0 / GL Shading Language 1.30 functionality can be implemented for this hardware. As Intel Linux customers were quick to discuss when sharing this morning there's now OpenGL ES 3.0 for Sandy Bridge (the embedded/mobile GL variant), driver developers quickly lose interest in older hardware.
One Phoronix reader pointed out this bug report with commentary by Kenneth Graunke from January:
Team Fortress 2 requires some functionality from OpenGL 3.0 and GLSL 1.30, which we currently only support on Sandy Bridge and newer hardware. Unfortunately, Ironlake and earlier currently do not.Basically, Intel Linux driver developers are busy working on newer hardware and other features, so missing functionality for older Intel products likely won't come. But since Intel does provide NDA-free programming documentation, other capable developers should be able to provide the said features. This bug comment was in response to Ironlake not working for Valve's Source Engine games on Linux.
It should be possible to implement the missing functionality on Ironlake. The code is open source, and the hardware documentation is freely available on the web(*), so in theory, anyone could make progress toward this.
Sadly, our team is extremely busy working on newer hardware and is unlikely to have time to implement GL 3.0 support for Ironlake...at least not any time soon. I sincerely apologize for this; we'd all love to see it happen too.
While I do own some Ironlake hardware, I would much rather see Intel working on the newer hardware support. Even if the Intel i965 DRI driver implemented the necessary GL3/GLSL1.30 features for the Source Engine games, it would still be damn slow. It wasn't until Sandy Bridge that Intel graphics really got their act together in terms of integrated graphics performance. Ironlake isn't too capable and the newer (and yet-to-be-released) hardware is much more exciting and will open new doors. Intel also, obviously, wants you to upgrade your hardware too.
So long story short, don't expect to see many Intel Ironlake "Gen5" and older generations of Intel graphics improved too much when it comes to their Mesa DRI driver. When it comes to overall reliability though on the Linux desktop for this older hardware, Chris Wilson at Intel continues to do great work on the xf86-video-intel X.Org driver and at least seeing that the older generations of Intel hardware are working reliably for a basic Linux desktop.
Intel's open-source team and Mesa in general is having a hard enough time as it is now with Sandy/Ivy Bridge doing only OpenGL 3.2 while the latest upstream Khronos spec is years ahead at OpenGL 4.3. Intel right now is employing 20~30 open-source Linux graphics driver developers but they are interested in hiring more talented Linux developers.