How to resume an unresponsive Ubuntu Desktop.

I am using Ubuntu 12.04 LTS with 3.5.0 Kernel. Sometimes the Desktop becomes unresponsive to mouse clicks and key presses.

Earlier I use to press Ctrl+alt+F1 login to terminal and reboot.

Then I read somewhere that I can kill all processes and re-login. The suggested command was:

kill -9 -1

Today I had the opportunity to use this command and it worked. The manual describes this command as follows:
EXAMPLES
       kill -9 -1
              Kill all processes you can kill.

I could re-login to the Desktop without reboot.