The existence of burn-in is not answered by debate and subjective evaluations which can vary greatly by mood, environment, and group think.
scott549 idea would be a sound test of burn-in and would demonstrate burn-in. I strongly support the idea of "brain-in" but have zero believe in burn-in, especially the way it's presented on Head-Fi.
If nothing else at least demonstrate a change in FR or distortion greater than the changes variations typically seen from changes in head or in ear placement.
Burn in for 100 hours? I don't believe it. Here's one reason for why. A brand new car needs, at most, 3000 miles of burn in for the engine. Given that people in the USA typically probably drive 30+ mph on average, even a car needs less than 100 hours of burn in.
Somehow a tiny moving diaphragm needs more burn in then a car engine which has so many moving parts that regularly expand and contract? They also rub against bearings and metal surfaces with nothing more for lubricant than a tiny bit of oil.