Many times we screw our gnome desktop panels accidentally. I found a very easy solution to revert them.
Just open terminal and type.
gconftool-2 --shutdown gconftool --recursive-unset /apps/panel rm -rf ~/.gconf/apps/panel pkill gnome-panel
But remember this is not the case when gnome panels get scrambled automatically (Which seems to be a consistent case in Ubutnu 10.04). You can simple refresh you gnome panels by doing.