I can confirm that the segfault was due to the absence of /etc/gdm/gdm .conf-custom after playing around with xgl/compiz. The instructions on the forums say that one should delete this file to disable xgl/compiz. It appears as mentioned above that removing this file causes gdmsetup to segfault. The solution is to restore the default /etc/gdm/gdm.conf- custom and reboot (or restart gdm).
-- gdmsetup segfaults https://launchpad.net/bugs/42712 -- desktop-bugs mailing list desktop-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/desktop-bugs
