To me, the break in period also includes the time it takes the driver to be come accustom to the new car. I've gotten good fuel economy from the beginning, but it gets easier and the average climbs after some time with the car.
On the subject of Ecoboost, I decided actually the diesel "econetic" is a better choice. It has less power 85 bhp, but probably just as much torque. Im just waiting for my dealer to get one in so I can drive one. It got 88 MPG in the government tests, probably closer to 75 MPG in the real world. Looks smart in Zetec S trim too.
I've noticed on fuelly.com that for a given model, often a prior year has better MPG even though the design has not changed...seemed to make no sense at first, but I realized the older cars are broken in is likely the reason.
I wish that site corrected for fuel types. The Focus for example is sold in Brazil and I bet they are using ethanol - MPG was terrible for the owner down there. And some cars skew the average by offering diesel engines. Most people do not use the filter to remove diesels (but at least they have a filter for that - but they don't do anything for ethanol usage).
I call bullshi* that they get better, but not like I have the data to back it up. If there is an improvement, it's so insignificant as to be a result of a tailwind or a downhill section of road, surely not because either one was "more" broken in.
I'm not sure about other models, but this is straight from my 08 Escape Hybrid's owners manual: "Your fuel economy should improve throughout your hybridís break-in period. As with any vehicle, fuel economy can be significantly impacted by your driving habits and accessory usage."
Well there is a 1.0 litre eco boost, which is probably too small for a truck, although it is available in the Focus. There is a 1.6 Eco boost available in the Fiesta ST with 180 BHP, so perhaps in the future you'll see that in some US trucks?