I was as much a skeptic as many of you with a science background. Then came the 2010 RMAF, where Nordost demonstrated their various speaker cables, beginning with a regular copper litz from Home Depot, and working all the way up to their top-of-the-line (Walhalla? Odin? I don't remember). Even my wife, who is somehow hearing impaired could hear the difference between the electrician wire and their lowest price point cable. It was really very obvious. When the demonstration approached higher and higher price point I could hear less and less difference, however: a clear sign of diminished return. But the first three or four wires sounded indeed different and increasingly better, in the sense of more musical. So, concerning the question about burn-in: if one hears a new cable, it might indeed sound different compared to what one was used to, so far so good: but after a few days of "burn-in" it begins to sound more pleasant until it finally hits its stride. Or so it goes. What about "ear burn-in"? Could it not be that the user's ear gets increasingly adapted to the new sound until - paired with expectation bias after a considerable outlay in treasure - final epiphany happens? That would put all the "burn-in" discussion onto a more human, i.e. physiological and psychological, level IMHO. Now, as previous comments pointed out, there is indeed a sonic difference not only between the type of metal in the conductor, but - perhaps even more importantly - the material of the insulating dielectric surrounding the wire. I was surprised myself. To my ears, and in my system at least, there is a clear audible difference between speaker cables insulated with PVC and those insulated with PTFE or PE. Following Maxwell's paradigm of the signal mostly traveling by modulation of the electric field around - and not inside - the conductor, the dielectric surrounding the wire will inevitably have some sort of physical effect; whether this effect leads to an audible difference, I can only say from personal experience: when I exchanged my Mogami Gold wire (with direct contact of PVC insulation around the copper conductor) to a single wire running in a PTFE tube, but not touching it (so, the dielectric being air), the sound became immediately "sharper", more "precise" and less "muffled", absolutely no question. I did many A/B comparisons, also with friends, and the difference was clear, not huge, mind you, but really noticeable. Since then, I have all my speaker drivers re-wired with a single silver-clad copper wire of various diameters running in a PTFE tube w/o touching it. My explanation as an organic chemist is that with PVC, the wire is surrounded by many large and "soft" chlorine atoms, "soft" meaning that the electrons in the outermost shell are quite mobile (contrary to Fluorine, for example, where they are strongly tied up and therefore "hard"). To me it seems quite possible, that these massed chlorine atoms somehow interact with the electric field surrounding the wire and its signal modulation. Maybe the physicists among you can put my conjecture on more solid ground?