Here is a quick trick that can speed up the main/navigation menus and menus in file manager like pcmanfm inside the lxde desktop. This trick is a setting for the gtk library.
1. Open the file named .gtkrc-2.0 in the home directory. If the file does not exist, then create one.
2. Put in the following in the file at the end
gtk-menu-popup-delay = 0 gtk-menu-popdown-delay = 0 gtk-menu-bar-popup-delay = 0 gtk-enable-animations = 0 gtk-timeout-expand = 10
Now logout and login. The menus should be very fast. The above settings actually control the user interface drawn by the gtk libraries.
Check the following page for a complete list of settings that can be mentioned in ~/.gtkrc-2.0http://library.gnome.org/devel/gtk/stable/GtkSettings.html#GtkSettings.properties