Yesterday I was trying Ubuntu Netbook Remix under Ubuntu 9.04 for my desktop. It somehow crashed quite often and not usable at all. I used the desktop-switcher (which comes with the ubuntu-netbook-remix packages) to set it back to the normal Ubuntu Gnome Desktop. It did not work well. The Gnome panel was in a strange state. Then I uninstalled Ubuntu Netbook Remix related packages. Things became worse. Normal gnome session became a empty desktop with only the background image. I had to go back to the termail (CTRL-ALT-F1), restart gdm and use LXDE instead.
Google came to rescue again. The following website has the instructions on how to restore the default gnome panel and it works for me. After three commands, I am back in business.
gconftool --recursive-unset /apps/panel
rm -rf ~/.gconf/apps/panel