I have been working with the developer of this excellent plugin for the backend:
http://www.yellowswordfish.com/index.php?pagename=admin-drop-menus-wordpress-plugin
He has developed a version of the plugin (for free I might add) that enables this across all blogs by dropping it into the MU plugins folder. It's a really great way to speed up your backend and give yourself some added funk over generic wordpress installs ;)
http://www.hadithuna.com/sitewide/muadminmenus.zip
You can see it in action by visiting my demo blog over at demo.hadithuna.com and logging in with username demo, password demo.
Enjoy!...oh and be sure to send a thankyou e-mail to this dev: andy(at)yellowswordfish.com