http://ignorethecode.net/blog/2009/03/21/context-menus-sub-menus/

Another thoughtful article from Lukas Mathis on menu design.  I found particularly interesting the comparison of the different ways to implement submenu mouse movement.  OS X provides a region you can move the mouse through on the way to the menu item without deactivating the submenu.  Windows isn’t quite as good, implementing a simple delay in the closing of the menu.  And the worst of all is most JavaScript implementations on the web, which require precise horizontal movement or the menu will close.