@Ronald Raygun:
Exactly, and this means that unlike the turbine, a
propeller does not *extract* energy from the air, it
*imparts* energy to it.

This is correct -- but only when considering energy relative to the
device itself. In the case of the DDWFTTW vehicle, the propeller
*speed up* the air relative to itself ('cause that's what propellers
do), but is *slows* the air relative to the ground (which is what has
to happen if we want to harvest energy).

Let's go back to the actively engaged skateboarder:

Let's suppose that the pedestrians on the sidewalk are originally
moving at 1ms. Let suppose that that the skateboarder is moving at
2ms. Obviously in this scenario, before the the pedestrians are
'grabbed' by the skateboarder they moving at 1ms relative to the
skateboarder AND 1ms relative to the ground. Once the skateboarder
pushes them backwards, bringing them to a complete stop, there is a
new set of relative numbers. Now, the pedestrian is moving 0ms across
the ground and 2ms relative to the skateboarder.

Pedestrian before contact:
Relative to ground: 1ms
Relative to skateboarder: 1ms

Pedestrian after contact:
Relative to ground: 0ms
Relative to skateboarder: 2ms

So, while the skateboarder *does* speed up the pedestrians (air
molecules) relative to himself, it slows them down relative to the
ground.

No one considers a wind turbine a PM device because we all know that
in it's wake is left a volume of air that has been slowed relative to
the ground. Wind that was going 10mph across the ground before it
encounters the device is slowed and is only going 5mph after it
encounters the device.

The source of the energy from the propeller driven device is
absolutely no different from a physics standpoint -- just as the
skateboarder leaves people in his wake going down the sidewalk slower
than before, the Blackbird leaves a volume of air in it's wake going
across the ground slower than it once was. Wind that was going 10mph
across the ground before encountering the device is not only going
5mph across the ground.