It would be a nice tweak if when you put your thumb all the way to the edge you would get decaying momentum on the cursor while you moved your thumb back into place to swipe the mouse forward again. And if you didn't go all the way to the edge it would stay as it was in the demo.. with some haptic feedback to let you tell the difference. I guess it would ultimately make it feel like having a thumb trackball.

There is no reason a touch pad can't be as accurate and natural as at least a trackball, which could already probably let you play Civ from your couch.. or quake

http://www.youtube.com/watch?v=a8Yky7WXrwU