How to create a top menu like the new Digg?

The new Digg menu is highly usable.

Take a look at http://digg.com/news/technology. Try to click on the down arrows to the right of each menu item on the top strip and you will see a menu folding down, with sub menus folding down as well. Also, all the contents of the menu are displayed in the second horizontal strip.

Improving the drupal core navigation to create a digg-like menu would be fantastic - it's very high usability.

Do you know of a drupal menu which is currently doing something similar?

Amnon
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Professional: Drupal Israel | Drupal Development & Consulting | בניית אתרים
Personal: Hitech Dolphin: Regain Simple Joy :)}