Driving a hybrid car is not as simple a relationship as it sounds, because to some extent the car drives you. That is, the feedback you get from the display on a Prius, showing you exactly how much fuel you're consuming moment-to-moment, can alter your driving patterns as you attempt to maximize the time you have a "99 MPG" reading.
That's certainly what happened to me. But the simple bar graph of the Prius is yesterday's news, as newer technologies take the concept of fuel-efficiency feedback to new levels. Via Treehugger, we hear of two of these: One is a Nissan gas pedal that literally provides "pushback" against aggressive driving. The other is a more organic, evolving display from Ford that responds to good driving with aesthetically pleasing visuals." The more efficient a customer is, the more lush and beautiful the leaves and vines, creating a visual reward for the driver’s efforts."
Both of these are cool ideas, but they're still just baby steps compared to the inevitable next generation of feedback. For one thing, while the Nissan pedal-pusher is supposedly drawing on various factors to determine when your foot is truly leaden, it doesn't take topography into account (i.e. the upcoming effect of an uphill or downhill) nor does it know if you're giving the car a lot of gas to prepare for a prolonged glide. I'm betting that future versions will incorporate GPS and trip-memory so that commuters who cover the same ground every day can get feedback that's tailored to exactly where they are and what the terrain has in store.
And as for the leaves, that's a great visual "reward" for the crunchy-granola types who are already buying hybrids, but if we're going to expand the market, let's think outside the tree: If the display featured a progressively racy striptease as a reward for fuel efficiency, you might see erstwhile Hummer drivers maxing out at 60, 70 or 80 MPG! Then again, if the display gets too enticing we might really be thinking outside the tree - as the car is wrapped around it. Back to the drawing board!