Give the scroll momentum to make it go faster.

One scroll activates the scrolling, but doesn't go very far or very quickly. Doing the scrolling motion again and again gives it more speed, and allows you to zip through long lists with great speed.

It's kinda like making a wheel spin with your hands. It works very intuitively on the N900. But make sure you press the screen enough with each scroll to make sure the screen registers it :P