This plugin is great and a must-have. The only issue is when you have too many plugins that add their own menus, like WP-Polls, WP-DB-Manager by Lester Chan, eventually the menus will run off the right edge of the screen and become inaccessible. When you point your mouse at them, the menus pop mostly off-screen.
I don't know if there's a way this plugin can detect the width and add a 2nd row if it gets too wide?
Aside from this, it's simply a must-have plugin!
http://wordpress.org/extend/plugins/ozh-admin-drop-down-menu/