Newly revised Toolbar with MenuButton (aero theme):
New menus (only 1 theme so far):
The menus include full keyboard support and work like desktop menus (no auto hide, they are click to hide).
The menus weigh in at 10kb which is much less than YUI 46kb + 40kb (container core). They may be missing a few features (like the menubar component) in this version, but it does support something extra I think will prove to be useful. Along with the built-in MenuItem types, items can be any HTML element and can be rendered from a template. This will allow Office 2007 style menus. I will come up with some example of this functionality before the official release.