I used to follow the manufacturer recommendations up until 2001 or so. I noticed every engine would use about a quart of oil between changes. On my motorcycles, I noticed stock to stock friends bikes were faster. Now depending on the type I do a much harder break-in procedure. For trucks like ours you need to let the rear-end lash for the specified time before towing. But I would drive it HARD unloaded. Not like a jack@@s but no babying. My truck maintains the same oil level on every change and thats the way I broke it in.
the BEST way to break in an engine though is on a dyno.