|Quoting Sovietjet (Reply 898):
Yes but Mythbusters did the "classic" scenario where the belt matches the aircraft ground speed. There is no way to test the original problem of the belt matching the wheel speed instantaneously. I didn't get to see the episode but AFAIK they were matching the plane speed. I'll watch it soon to make sure.
(I know it has been beat to death over and over and over but...) the test was fine because it doesn't matter how instantaneously the belt matches the tire speed, there is still no significant force to counteract the aircraft's thrust from moving the aircraft forward. The wheels are simply spinning twice your forward velocity. Imagine skiing down a snowy conveyer belt that was moving up hill. Doesn't matter how quickly that belt matches your speed, gravity will keep accelerating you forward, same thing with the thrust of an aircraft.
I think they did the best practical test of your OP that could be done in the real world.
Awseome! I got the 900th post!
[Edited 2008-01-30 21:51:54]