I've often wondered how a solid state piece of equipment could have a break-in period. What changes and if something changes over time how does the manufacturer/designer account for that change? How would a manufacturer assure consistent quality if all their gear was changing after the customer turned it on? If something does change is it noticable (keeping in mind significant figures)? My thought is that over time we grow accustomed to the different sound of the new equipment and it becomes our new norm. This would be particularly true when we change from one well made piece of gear to another. My expectation is that the gear comes out of the box meeting the specs and that they are consistent over time.

Those questions/comments aside, I agree with Ritz's comment about operating temperature, though I've noticed it takes minutes not hours to reach it.