It took me a while of googling to find out how to enable dri support on ati cards. /dev/dri/card0 belongs to root:root with 0660, but should belong to root:video or root:users depending on taste :) One needs Section "DRI" Group "video" Mode 0666 EndSection in the xorg.conf, and it has nothing to do with the udev settings, which look perfectly ok, with /etc/udev/rules.d/50-udev.rules: KERNEL=="card*", NAME="dri/card%n", GROUP="video" This should be documented somewhere, i'd opt for a warning in the opengl-update script, or a note in xorg.conf.sample, unless there is a good X11 installation document, which i have not found.
*** This bug has been marked as a duplicate of 63580 ***