If you’re doing some tests on your Gnome or KDE panels,you may need to reload the panels frequently for the effect.Instead of restart computer or re-login,reload the process would be a better way.
For ubuntu gnome,press Alt+F2 key combination and type following to kill the process:
It will immediately restart the panels,or you can run gnome-panel to start it.
For ubuntu KDE,also press Alt+F2 key combination and type following
dcop kicker kicker restart
Run following to kill and restart the process if the kicker panel is locked up.
killall kicker kicker