What could you really do to boost the engine....without voiding the warranty?
The engine is clearly (unless you constantly floor it and maximize torque) slightly lacking on "boogity boogity" however, we do know that it was designed for fuel economy. I prefer to drive very conservatively. I prefer to keep the RPM's at or below 2500 (this delivered consistend mileage in the 34 to 38 mpg range on my 08 Focus, delivering this at a maximum 60 mph.
I have pushed this car, and driven it conservatively, and strangely enough, fuel mileage slightly improves closer to 3000 RPMS....Mileage is at 2300 and overal average is 35.9 mpg overall (according to the computer in the car) my fuel reciept calculations mirror this. Reached and maintained 46 mpg on a 600 mile road trip.