If you try out the latest Ubuntu Jaunty (which is not officially out yet, and I would not recommend for your main machine, where you do important stuff on… seriously, get Intrepid or Hardy if you want something stable), you might be surprised by the fact that you can’t bail out of X with Ctrl-Alt-Backspace anymore…
Apparently some people thought it was too easy to trigger by mistake, and now it’s disabled by default. That of course isn’t that bad.. but there’s no easy way to enable it again. No GUI tool, nothing. (there is a hard way if you want, though)
Now, granted, you can just switch to a tty, log in, and restart the X Server from there (well, if that still works… if the X Server is under much stress switching to a tty might not work as expected), but Ctrl-Alt-Backspace is much more convenient and will work in most cases, and might save you from a forced reboot if that works and switching to a tty does not. It has it’s uses, and is usually needed in an emergency if the X Server starts misbehaving.
So, here’s hoping that they implement a GUI tool so you can start using Ctrl-Alt-Backspace if you want again, without editing scary configuration files.