We're talking about OIL here, not gas.
Peter
But it is a similar sounding argument -- ask 10 different people about it, and you'll get 17 different opinions.
Same thing with the oil change interval debate.
That being said... Here is my $0.02 on engine break-in:
Don't beat on your new engine. But don't baby it either.
Parts in your engine stretch, compress, and bend. And they do so more at higher RPM. You do need to get these parts properly worn-in at their limits, both high and low.
A little idle period when you 1st start up to get all the fluids circulating. Some gentle driving to get everything up to operating temperature. Then drive at varied RPMs and loads -- including the occasional romp on the loud pedal to the redline.
So as long as the motor is good and warmed up, don't be afraid to hammer it going down the local on-ramp.
And just like not beating on it right after you start, don't hammer it right before you shut it down. Let temps stabilize before you turn the motor off (especially you EcoBoost guys).
After the first 1000 - 1500 miles, change the oil and filter. A lot of wear is happening in these early stages, and I figure it's best to just get the debris out of there.
The worst running engine I ever had was babied too much during break-in. I thought the gentle life it had would be a benefit, but as soon I started to drive it in a more spirited fashion than the previous owner (yes... a "little old lady") I got issues -- oil blow-by, down on power, poor mileage, valve train noise. It was GM's bulletproof straight-6. They would outlast the car they came in. That one needed a rebuild at 55k miles.
And BTW...
Bigdude2468 is absolutely right.