Running-in
Forget revs, it's the amount of load that's crucial.
Running-in any motor properly makes all the difference to long term performance and smoothness, even with modern machining methods. You can rev it high, but never with full throttle or for prolonged periods, also never lug them up hills, get into a lower gear and keep revs up using low throttle.
The ideal running in regime - You need the revs to free things up and make sure there are no high spots but not loading the engine by giving it too much throttle.
It was always suggested to me that the actual revs are not a problem within reason as long as the load on the engine is not high, so running along on half throttle down hill at near max speed is better than lugging up a hill in top "keeping the revs down" !
Heat build up is the enemy when running in. If you do a long run while running-in, vary your speeds and stop once in a while to let things cool down.
I agree with Pieman, there's a school of thought that recommends full throttle occasionally for short bursts during the initial period of running-in. This is to ensure that combustion gasses get well behind the piston rings and force them onto the cylinder. This removes the last of the machining roughness and beds the cylinder and piston rings in properly.
Failure to do this means that the cylinder walls will glaze over and cylinder pressures and therefore compression will be lost in the future. No real damage, but lower performance.
Make the engine work, but don't let it slog and don't hold full throttle for too long. Increase the work load gradually and let the engine rev or even reach high speeds on downhill stretches and light throttle openings.
The art of running-in is to keep the motor "happy". To do this, free use must be made of the gears.
The accent should be on gradually increased work loads until full throttle is obtained.