I have an advanced mini docking station with a DVI powering my LG 24" LCD. Usually, I like to use the Gnome Monitor Resolution Settings utility to turn off the laptop screen and keep the LG 24" on instead. The problem is when I want to take my laptop out of the docking station, I need to turn off the LG screen and turn on the laptop screen. When I do that, X crashes and I lose all my open windows. This sucks because I have lots of those windows open with files and such and it is a a pain to do that. After some researching, I figured out that if I tell Xorg to turn off this "Unknown" screen, turning things on and off does't cause a crash.
To do that, I added the following to my Xorg.conf (found in /etc/X11/):
Option "Ignore" "True"
Option "monitor-HDMI-1" "HDMI-1"to the device section of my file.
Now when I run the Gnome Monitor Resolution Settings Utility, I get: