I would categorize charging as different. Yeah, I've heard the charging issues, I would have called that "warm up" rather than "burn in".
Alright, maybe "dramatic" might be overstating things, but it does seem to take a while for what little change to occur, even if it's just a slight smoothing out of the high frequencies. There's a difference between burn-in taking a long time vs. creating a huge difference, I usually try to phrase my descriptions carefully as to when a difference is huge vs. subtle, and whether or not it's significantly audible vs. not.
In fact, a lot of times, it's not significant. I can count on one hand the times it has been significant that I have heard (bass on silver cables, the bass in a certain pair of headphones, several components [including a set of tubes] becoming smoother, and...uh...not much more that I can remember).
Does that make sense?