Awesome! Having suffered thru setup and usage of YUI menus this will be a welcome alternative.
The problem I was trying to solve involved dynamic context menus- that is, when you right-click on a table row an ajax request is made to retrieve the appropriate menu items and submenu items from the server. The problem I ran into with YUI menu is that it is very heavy and difficult to optimize for this purpose. It worked well for static menus, but these dynamic menus were a nightmare.
Have you considered this case?