Droopystop,
There really is no ground cushion, I will make that Myth #11, Thanks!!
We bashed this around quite a bit in the past. The ground effect is due to the aerodynamic effect the ground plane has on the flow under the rotor. It reduces the angle needed to achieve the lift, and it reduces the induced drag/power of the rotor.
The pressure under the helo in a hover is NOT higher than somewhere else, and the aircraft is not perched on a ball of high pressure air.
Myth #11:
The helicopter is perched on a ball of high pressure air when close to the ground, and "falls off" this ground cushion when it moves forward.