The latest Xorg video driver for Intel chipsets will probably cause a slowdown in rendering due to a switch from TTM to GEM. GEM is only supported in kernel 2.6.28 and above so it’s recommended that you stick with drivers released before 2.4.3.
More information: http://bugs.freedesktop.org/show_bug.cgi?id=13922
http://www.x.org/wiki/ttm