lame,
just action/reaction - no downwash making things tricky. They push off upwards creating a downward force on the plane which reacts accordingly, then for a moment the plane has to produce the weight of passengers + cabin luggage kilos less lift while they are in freefall inside the cabin and will rise. Then floor and passengers reunite happily and everything is back to normal, same energy state as before.
You were joking I guess but someone probably is wondering...
Then again, there's PFIL(*) and that can be empirically proven... eh... sorta...
Cheers,
/ft
(*) Passenger Fear Induced Lift, short version: Passengers hold the plane up by clinging onto their armrests and pulling. The more scared they are, the more they pull. The take off roll is necessary to produce noise and vibration enough to scare them. Flaps create additional noise/fear/lift. It's pretty scary to see the ground swoosh by a few feet below so we get ground effect...
(Editd fot typos)
[ 15 August 2001: Message edited by: ft ]