So I upgraded to jaunty and turns out that the intel driver 2.6.1 + libdrm-intel 2.4.4 (that perhaps is not precisely libdrm) makes opengl run SLOW; apparently based using software rendering; while intel driver 2.4.1 + libdrm 2.3.1 (from intrepid), everything is perfect and performance is good.
In one line: libdrm-intel 2.4.4 + intel driver 2.6.1 = slow opengl (apparently being rendered with software); libdrm 2.3.1 + intel driver 2.4.1 = good opengl.
Am I missing something, or perhaps there's a dependency on a more recent version of something?
I must correct myself, kernel 2.6.28 was necessary to get a good performance. Although, the performance has indeed degraded a bit, like 10fps less with glxgears maximized to my 1024x768 screen.
Marking invalid, will report a new one if I find a bigger regression.