well, it is a good idea to let your motor run at idle for a while with a brand new engine (well, i know that at least with motorcycles you have to idle them through a full tank of gas to let the gaskets and pistons get "burned in" if thats what you want to call it) but as far as CPU burn-in goes, i really dont think that it matters, because the only thing that could possibly change with "burn-in" time would be the metal expanding and contracting, which it is going to do anyways i dont know, its like gummy up there said, i think that it is just a catch phrase