A note on the eyewitnesses. I live in Connecticut, and was watching tv when the reports of the crash started coming in. Various witnesses called in. Some reported seeing the right side engine fall off, some reported seeing the left side engine fall off. I don't believe that any of the callers I heard claimed that BOTH had fallen. Also, no one said a thing about the tail of the aircraft - the closest anyone came was one individual who claimed that a wing had fallen - in retrospect it would seem that what he actually saw was the stabilizer and/or rudder.
In this case, I would tend to believe the NTSB that this was not a terrorist act, (although they may be trying to blame the pilots for something that might be at least in part due to a structural weakness.) Please note that I am not one who blindly accepts their findings - I still believe that something hit flight 800.