This function makes adding custom menus to a theme very easy, but the theme needs to support it as well; and, the posts are written to help with the upgrade process. Stop by WPFirstAid.com and click on the wp_nav_menu tag.
These posts have also made me put on my latest to-do list: update all of my themes to use more of the new WordPress 3.0 features. The published themes will be first followed by my personal custom versions I use on my various sites.
I am also busy with the WordPress.org Theme Review Team, too.
How is your July shaping up?