I recently had a chance to compare a very close serial number pair of LCD3 to my pair. (They were purchased about a week a part.)
Surprisingly there were quite a few differences I noticed between the two:
1) His pair was louder at the same position on the volume pot than mine, making his more sensitive
2) His pair was more linear across the frequency spectrum
3) His pair had slightly more detail but leaned on the bright side, with a slightly wider soundstage
4) My pair literally has 2.5-3x as much bass presence and impact as his pair (which I throughly enjoy).
5) My pair are smoother in the highs, but slightly less detailed.
6) From an aesthetic point of view my pair have the nicest wood cups I've yet seen, almost perfectly symmetrical and a cinnamon brown color.
7) In a way, they almost sounded like different but similar headphones.
I am not much a believer in headphone burn-in, but in case any of you are his pair had about 120 hours on them whereas my pair has about 10.
His earpads were also more broken in and squishier.
Any thoughts on why?