I've heard it when I've been too busy to think about the new component (and therefore didn't expect to hear break-in but heard it nonetheless, so then how can you make a "placebo" argument?).
The effect here is not really analogous to placebo. What it boils down to is that we know for a fact that human perceptions - and even physical things like getting better from an illness - are strongly influenced by some bizarre and very complex combination of beliefs, circumstances, expectations, etc., often in highly unexpected and non-intuitive ways. Therefore any time you try to base much of anything on people's anecdotal accounts you have to be aware that there's a good chance something psychological is affecting them one way or the other (read up on the unreliability of eye-witness reports, for example), but you can never have much confidence about
how or
why they've been affected.
Now when people report something which we're pretty sure is true, we don't need to worry much. Like if everyone says the sky is blue on a clear day, that's probably because the sky really is blue. But when some group of people make a claim that goes against the grain of what we know scientifically, particularly in an area as well-studied and quantified as electronics, we have to take it with a grain of salt. That
doesn't mean it's wrong, or that we should ignore it - just that we need to do some controlled tests to remove the effects of expectation etc. And it's really easy to do so in this case - all you need to do is run a blind listening test. Easy as pie.
If that blind test shows no difference, well... there probably wasn't one (if you don't agree, I recommend shaving with a new brand of razor, manufactured by Occam). If it does, great - we just learned something important and possibly profound, and engineers and scientists will have to sit up and take notice.
