Option to auto-hide the menu. Only show it on mouseover

Allow to auto-hide the menu (like the option to auto-hide the windows taskbar). Auto-hidden admin menu won't occupy screen real estate and will only be visible when needed - on mouseover, or when the key combination is pressed.

I'm not sure if this issue belongs to admin_menu or to admin_menu_dropdown so I've opened it for bothe modules (here is the other issue: http://drupal.org/node/367878).