Since my upgrade to Gutsy, I encountered time after time that X-server crashed whenever I pressed the keycombination of shit+backspace. After some reading, it turned out that this behaviour is caused by XGL. I fixed it like this:
~/.kde/Autostart$ echo "xmodmap /usr/share/xmodmap/xmodmap.us" > disableXbackspacecrash
~/.kde/Autostart$ chmod +x disableXbackspacecrash
~/.kde/Autostart$ ./disableXbackspacecrash
Of course it was needed to restart kde first, before changes were taken into effect.