FWIW, I implemented inertial scrolling (or flinging) on the timelines at http://www.preceden.com. You're welcome to check out the JavaScript if you're interested in implementing something similar.
It was exciting to set up... really brings you back to high school pyhsics.
Hah, funny you should mention that. I noticed it when I stumbled across Preceden a month or two back, but it's always seemed a bit buggy, and put me off trying out the site. In Firefox & Chrome, if you drag the timeline to one side and hold in place for a bit, then release, it scrolls as if I hadn't held it stationary.
It was exciting to set up... really brings you back to high school pyhsics.