Regarding the on-board display that tells you what your supposed mileage is, has anyone indulged in perusing the Owner's Manual about this?
I would like to know what the Owner's Manual says about the calculated average mileage. I bet that there is a disclaimer in there that effectively says that the figure you see is average to give you an idea and not a spot-on actual figure that you can wholly rely on.
I do laugh though when people start to say "how do I get better mileage out of my WRX or STI?" Well honestly, you bought the wrong car if that's what you seek.
I do cringe and feel afraid to be on the roads when people start to say "that I 'hyper-mile' by disengaging the drivetrain or I shut the car off completely and coast downhill". Just wait when you're in an unexpected and/or panic situation and guess what? the car is in neutral or off and you can't do a damn thing except to further the problem. Saving fuel at this point is a small item. Being an idiot is a much, much larger item.
Back to the mileage reader: it's a marketing tool and gets a lot of response in this day of higher per-gallon gasoline prices.