Whatjd: I have entertained the same question you pose, being the perpetual skeptic. The ear-brain connnection can become used to many things, and over time adapt to what it thinks is "normal". Much the same thing happens with smell if you are exposed to an aroma long enough (and it's not lethal), you lose your awareness of it. This is due, in part, to what is called the reticular activating system (RAS), which is the threshold above and below which things become noticed. For example, you are not normally aware of the sounds or sensations of your own breathing, because they are below the "alert" level of the RAS. However, I recently have had an experience which makes me re-think the notion of "burn-in" versus getting used to a sound. About 4 months ago, I bought a new Bryston 4B-ST amp, and both my wife and I thought it sounded cold and rather etched. I nearly sold it, but decided to give it some time to "burn in". My wife rarely listens to the sound system other than to watch TV or the occasional DVD. After 6-8 weeks, I had the distinct impression that the amp sounded a lot better - more transparent, better balanced from top-to-bottom, and and less "white". I asked my wife to listen to the system on some music she knew well, and she was startled at how much the system sounded. She asked me if I had added a new component, or done something to improve the system. In this specific situation, there is no doubt in my mind that something actually happened to improve the quality of sound coming from my system - call it "burn in" or whatever, but it was NOT simply becoming used to the sound.
