My sister has the trip computer in her Corolla. She's happy to be getting around 35mpg. I think I'd be less than satisfied with anything less than 45mpg in her car, but she does have to drive a lot of miles, and at least she isn't driving her husbands Durango that only get about 17mpg.
My Town & Country is the first car I've had with this option, and it's made a huge difference in the way I drive, so if it's in every car, it will make a difference for some people, and sets a precedent that other manufacturers might feel obligated to follow.
Better than an idiot light, but if an idiot gauge just shows you how much of an idiot you are, undoubtedly some people will choose to ignore it. Maybe they should just make fuel tanks smaller. If you drive like an idiot, you have to stop 3 times on your way to work to fill up, but if you "adjust the nut" you can make it to work and back.
