If you drag and release quickly from the horizontal menu, the menu will auto slide for a distance. It seems to slide more the faster you drag and release. Source ->appear.dk
How do i achieve this effect? Has it got to do with some complex formulaes?
This technique is called kinetic scrolling (you simulate kinetic energy). Since the dawn of the iphone this technique has been hyped, though it can be used on mobile devices with great benefit, I would refrain from using it inside a website (like all other sorts of scrolling)
However, here's an easy to use jquery plugin: Here you go