I have never "burned in" a PC, neither a complete assembly, nor an upgrade. Can't say I've seen a need for it, as everything seems to run fine on the one's I put together. I test multiple programs, and will often run a program or two through the night if the destination requires such usage just to ensure as few problems as possible will arise. Perhaps this is all burning-in is.
Kill a man, you're a murdered. Kill many and you're a conqueror. Kill them all, you're a GOD