This blog post gives instructions how to get rid of the GNOME panel menu delay, i.e. the small delay one experiences when moving the mouse pointer over the System menu, and the submenus like Preferences and Administration don't open immediately. The solution shown has been tested on Ubuntu Lucid, but it might work on other systems as well.
Run the following command to configure newly started applications to omit the delay:
$ echo "gtk-menu-popup-delay = 0" >> ~/.gtkrc-2.0
Run this command to restart the GNOME panel currently running:
$ killall gnome-panelIf you are interested speeding up the loading of icons, see more information on http://www.ubuntugeek.com/how-to-make-gnome-menus-faster-in-ubuntu.html.