I accidentally deleted the GNOME bar while messing around with it. I could have rebuilt it by hand, applet by applet, but I thought that there must be some way to reset it back to the default. It turns out that this is a pretty straight forward thing to do.

In the /etc/xdg/menus folder are the templates for the default menus. The one we are interested in is "applications.menu.orig.dpkg-new".

Simply copy this file to your /home/<usr_id>/.config/menus/ directory and then rename it to "applications.menu"

I got this tip from the following forums:
http://forum.ubuntu-fr.org/viewtopic.php?id=199923
http://ubuntuforums.org/showthread.php?t=335675