In seriousness, I should point out some things about the F4/concrete block video, and what happened to the debris. I too initially thought: where did it go?
The aircraft in the video is an old (1958-1979) military jet. These are typically made out of stronger materials and heavily armored as they get not only shot at but subjected to stronger physical forces.
The Boeing 757-200 was first built in 1983. Civil airliners are made of lighter materials and designed for efficiency, not survivability, as you would expect. This is especially true of modern aircraft; I discussed this at length with some aviation engineers after the recent talk of introducing air marshals, and the general concensus was that with new thin-skinned airliners, a single bullet impacting the fuselage would have disastrous potential.
The video is from Sandia and you can get stills and information at
http://www.sandia.gov/media/NRgallery00-03.htm . The website there states that the experiment was carried out with the jet fuel mass replaced by water. This negates any effect of fire and fuel-driven explosion which would have further destroyed any intact debris.
It also states that "The test established that the major impact force was from the engines" which is demonstrated in the Pentagon aftermath. There are neat round holes/tunnels running through the building where the engines have passed. One of the conspiricock presentations asks "are we really supposed to believe that the engine punched a neat hole in this wall?"
The answer is "yes". The engines are the only significant solid part of any airliner. Their disproportionate mass means that they therefore going to maintain more inertia than any other part of the aircraft and thus, essentially act as a battering ram on anything they encounter.
Here's two picture of a tower block hit by a larger 747. The website I found it on is a proponent of the conspiracy theory but in actual fact I think it supports the official account.
http://members.shaw.ca/freedomsix/pics/w921004-1.jpg -- the block
http://members.shaw.ca/freedomsix/pics/donley_z.jpg -- close up
757: 220,000lb max weight., 38m wingspan
747: 775,000lb max weight., 60m wingspan