For some reason my top and bottom panels have disappeared. I can't right-click and add a new panel either. I tried executing gnome-panel from the terminal, rebooting, but no luck. Any idea how to recover these panels?
Turns out that uninstalling Evolution also removed gnome-panel (?!?). I rebooted in recovery mode, then dropped into a netroot shell (terminal with net access) and installed gnome-panel via apt and the panels returned on the next normal boot.
Hope this helps someone else.