cleandog and others: the engines are ALL run-in at the factory following assembly, on the dino. Basically they rev the **** outta it for several up-down cycles - the idea is to get the revs really high, then go completely off the throttle which creates the force necessary to seat the piston rings.
After buyers take possesion of the vehicle, most of the break-in process has already occurred and the 1200 mile break-in period is precautionary and just puts the finishing touches on the process.
However, cleandog to error on the side of caution with your very expensive new vehicle, I would adhere closely to the recommendation in your owners manual and as posted above.
DO NOT drive for extend periods of time at one rpm/speed on the highway - this is very clear and I would not recommend ignorning this warning - why take the risk? No, it won't cause your car to have a catastrophic failure, but if your vehicle is not broken in properly in its early life, it can lead to slightly lower efficiency, power, oil consumpiton and longevity, most of which won't be noticed for many years but nonetheless it could make a difference.
Have you ever wondered why there is a lot of variation in the fuel economy people report, even though they all drive the exact same vehicle? The same goes for performance, oil consumption, and longevity ex. one guys says "my Pathfinder ran for 300,000 miles", and the next guy says "my Pathfinder died at 150,000 miles of engine failure". What's the difference, same vehicle, should get similar results, but that's not the case! The big difference is how the vehicle was cared for in terms of driving habits, and maintenance.
Driving habits start the day your purchase your new vehicle, and include how it is driven when within the break-in period. Yes it may be Nissan being cautious, but rightfully so. Would you want to be wreckless with your new vehicle? No, then closely follow the break-in recommendations.
In the example of highway driving, DO NOT use cruise control, and don't hold a constant rpm for more than say 10 minutes at a time. Every 10 minutes just step down on the throttle a little bit, bring the rpms up to say 3-4000, then completely let up on the throttle and coast for a few seconds back down to cruising speed. Its the hard throttle followed by no throttle/coasting that will help seat those piston rings. And DO NOT floor it to pass, higher rpms are ok, but beyond 4000 with flat out full throttle you can do damage - the engine and trans are very tight still and aren't ready for full throttle pressures.
Just follow the break-in procedures to the letter and you'll be fine for the long term!!
