Okay app nerds, here is an idea for a good one (though probably not a profitable one). Today's fuel efficient cars are fuel efficient in very different ways. Diesel cars tend to be very efficient at constant revs but less so the revs vary a lot, thus they are great for highway driving, less so for city driving. Hybrids are the opposite, the electric motor does a lot of the heavy lifting in the city but the gas engine has to kick in on the highway.
So what car is right for your particular driving habits? A lot of us can make some generalizations about our driving and many might be able to point the car to purchase if our goal is to burn a little fuel as possible. But there a probably lots of folks like me whose driving habits don't provide a clear cut answer. For those people I think the new smart phones can provide a precise answer.
The app would be simple, keep track of city versus highway driving by using the GPS function of the phone. Feed the data into a simple algorithm that computes combined fuel efficiency for your particular driving habits for every car for which the EPA provides fuel efficiency estimates.
Shazam! Here are your top 5 fuel efficiency choices.
Brilliant! I think I am the second coming of Steve Jobs, perhaps Apple will call...