This tip is too useful not to share. Running a computer lab with GNOME (Ubuntu GNU/Linux in my case) means desktops sometimes go haywire as my students are given the freedom to play with the panels and other settings. Resetting the desktop to its default condition is very easy:
Browse your home folder, view hidden files, and delete any of the following that exist…
.gnome .gnome2 .gconf .gconfd .metacity
Log out and the next time you log in, your desktop should be reset.