[update: read below to see why I'm wrong]
I just finished watching the plane on a conveyer belt myth (I had TiVo'd it) and am rather disappointed.

There was one key problem that they tested the myth improperly.

That is the whole myth revolves around the plane staying in place relative to the surroundings off the conveyer belt.

You see, when you see the plane take off, the plane is moving PAST the road cones. This means the plane is NOT staying in place and that the plane is traveling faster than the conveyer belt is going backwards. The easy way to see this is that the only way it should have passed those cones is if the plane had already taken off.

For the myth to have been properly tested, the plane should not have moved in relation to anything off the conveyer belt (including the cones it passed). The ONLY myth they busted was that the plane could take off on a moving conveyer belt so long as it could speed up faster than the conveyer belt is going backwards, which is obvious... Assuming the car Jamie was driving was going 25 MPH, and the plane needed a relative speed of 25 MPH to take off normally, then all the plane would need to do is speed up to 50 MPH... Relatively it is still moving forward in relation to the air (and road cones for that matter) around it at 25 MPH and would take off...

This isn't the myth they were given to test, but they didn't seem to understand that... The myth is if the conveyer belt matches the speed of the plane going forward AT ALL TIMES (not the take off speed but the actual speed of the plane at any given second), so the plane stays still in relation to the ground around it, will it take off? The answer to this myth is obviously no.

Perhaps the only argument between people who disagree is a misunderstanding as to what people arguing... I would have never doubted a plane could take off while on a slow moving conveyer belt assuming it could relatively overcome that speed, but if the conveyer belt matched the plane's speed at all times, the plane couldn't get off the ground...

[update]

Okay, so my first comment here proved me wrong on this issue. I had a complete misunderstanding of what was happening, and the comment made here made it clear in a way the episode did not.

The conveyer belt has ZERO effect on the plane, or rather, an infintesmal effect on it. So if you ran the conveyer belt at 100 MPH, the plane would completely ignore the belt. That is because the wheels have no effect on the plane, they free spin and the propeller still pulls the plane forward. Ideally if you got the conveyer belt to go fast enough, it could have an effect on the plane, due to the friction the wheels cause. But we're probably talking speed of light type speeds for the conveyer belt to have any effect. But I'm kind of right on one issue. You see, the plane can only take off if the conveyer belt is long enough for the plane to take off normally. So if you put it on a treadmil, the plane would just fall off the end...