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You installed Ubuntu, and since it's so darn configurable, you decided to try a whole lot of different settings and configurations. Maybe to the point where things just aren't as they should. How do you restore your desktop to it's original state?

If for any reason you need to restore your desktop to its default state, open a terminal and run these commands:

cd /home/username – This moves you to your user's /home directory, (which you should automatically be in when you open a terminal anyway), be sure to put your user's name instead of /username.

Then:
rm -rf .gnome2 .gconf .gconfd .metacity – This command erases/removes all your gnome-desktop configuration files, forcing a re-spawn when you re-boot. It's safe and effective.

Here's an Ubuntu Forum thread discussing the procedure: http://ubuntuforums.org/showthread.php?t=1060406

On a similar note, when installing Ubuntu or any other Linux OS, if you take the time to install a separate /home partition, restoring can be done at a deeper level.
Essentially, if you've installed a separate /home partition, you can re-install the entire operating system without over-writing your folder, documents and other important data.

Here's a link to Installing Ubuntu with a separate /home partition.