It's one of those things that's easy to validate conceptually, but in practice it doesn't necessarily work well - at least not right away.

The standard way is that you scroll/swipe on a trackpad to move the view. The scroll direction follows your eyes which is also the rectangle surrounding the document and also equivalent to the direction you'd move the scroll bars.

The new model draws a parallel to the physical world where you're moving the content. IMO, even though one may get used to it, I don't think it will ever be as natural as on a mobile device, mainly because you're not actually touching the content when using a trackpad. That disconnect makes a huge difference. I may try getting used to it for a few weeks after I finally install Lion on my boot drive.