For everyone’s reference, it appears that you MUST use the menu manager supplied with the Display theme in WP 3.0. If you try to use the new menu manager provided by WP (under Appearance > Menus), the menus will not load properly. The menu would appear but disappear as soon as you hovered over it. Occasionally, I could get it to stay open but not for more than a second — this made it impossible to click anything. In addition, the side-bar menu will NOT work if you use the WP Menu system mentioned above. Stick with the menu manager under the Display Options system.
Has anyone else had this experience and/or do you know how to fix it?