Can you try move the relevant mesa driver to a different directory so we can see if it is the x driver or the mesa driver that is triggering it?In other words move /usr/X11R6/lib/modules/dri/i965_dri.so to a different directory outside of the ld.so search path. Your x log should show the software renderer 'swrast' being loaded.
This helps. I could not get a hang anymore. Youtube looks good again as well.
