"Someday we will all unite and take over the world and Mike Walker will be in charge of the headphones SS that wipes out those poor people silly enough to have negative opinions on the hd600's bass response."
I can't help but to feel that you are setting the bloodhounds on my trail. What did you say about "making enemies"? Grrrrrrr. Very often, Mike is making an awful lot of sense, though:
"Our opinions are intimately tied to our experiences, and perceptions!" Exactly.
I agree with JohnActon as well: "I also believe personal taste is an exponentially bigger factor in preferring one headphone over another than any combination of physical traits that may be in a position to influence one's hearing (shape of ears, aural acuity, etc)."
We always tend to compare equipment with our experiences in similar situations. It is a learning process, there is an "audiophile" or hi-fi socialization. I had started a thread about this in the General Discussion section and I would like to hint at an article from the "Stereophile" archives once again, that, I think, has a lot of relevance in this context: God is in the Nuances
by Markus Sauer. He reports about a psychological experiment dealing with the striking differences between concious and emotional reactions of audiophile listeners. It seems, we do not necessarily know, what is good for us, we can unlearn musical enjoyment.
I do not believe this issue of fit (back to the original topic) is as important and decisive as you think, but there is definitely an effect from it. I usually prefer wearing circum-aural headphones shifted to the front of the head, with the drivers' axis aiming at a point slightly in front of the ears. The sonic changes are minute and not as drastic as differences between headphones, but they are there: often, the soundstaging becomes somewhat more natural with more in-front localization, and a certain harshness in the treble seems to disappear. This effect could be more pronounced with headphones that have their drivers positioned relatively close to the ears (Beyer 990 Pro) than with designs like AKG K501 or Sennheiser HD 580/600. With supra-aural headphones, by the way, proper positioning is almost crucial, I think, because interaction with the outer ear is even more immediate.