Results in content truncated. Truncated region can sometimes be accessed by flicking down from the top. But when a touch is registered on truncated regions, it will snap back to the top, and subsequent scrolling fails.
This behavior is observed in the demo as well: http://static.uxebu.com/~david/touchscroll/alpha/
This is observed on iphone4 safari browser, latest update (as of dec 2011), and on chrome (desktop).