Seriously, one of the clever parts of the hybrid system is what I like to call the "social engineering" aspect-- prominently placing instant and intermediate-term mileage guages on the dashbord makes the driver constantly aware of the mileage he/she's getting.  Driving my Civic Hybrid is like driving a video game, and I'm always doing what I can to increase my mileage at any given time.

If you want to get better gas mileage, follow a hybrid driver.

Some in a prior post suggested putting in a vacuum guage, which would do something similar.  

This is a really great idea!  We could even have an idiot light version.  A "Poor Fuel Economy" light that goes on during situations where you are getting worse mpg than normal, for whatever reason.  Maybe this could be a three LED "MPG" light, with red for poor, yellow for normal, green for good.

This is the sort of thing a behavioral economist would come up with.  With just a tiny bit more information, we can tell the motorist when they are wasting money.  Since people hate to waste money, they would have a strong incentive to keep the yellow or green light on.

This would be require only a simple change in manufacturing regulations, could be implemented quickly, and would help reduce the consumption across the spectrum of vehicle types.  My experience of driving cars fitted with these devices is that is difficult to ignore them, it is very human to try to improve your score.  Without really being aware of it, you learn a driving style which maximizes consumption.  I find myself using exactly the techniques I learnt even though I now drive a car without a meter.
Another "pain free" change could be that manufacturers are required to published detailed consumption graphs - ie consumption in various gears / speeds.  Many people are not aware of the massive increase in fuel use which occurs between 50 and 75.
This may be academic - once consumers begin to feel real pain they may demand these improvements.

Apologies to Ben, who said something very similar a few posts down and a half-hour earlier.

I have a 2005 volvo suv guzzler (purchased before I learned about PO) that allows me to toggle between ave mpg, instantaneous mgp, and miles left in the tank.  I spend so much time trying to maximize my instantaneous mpg that I've probably become a driving hazard.  It has, however,  taught me to use my lead foot sparingly.

I installed a ScanGauge in my VW TDI diesel Jetta.  It plugs into the OBDII connector and shows, among many other things, instantaneous MPG and current trip MPG.  I discovered that putting the transmission in neutral when coasting down hills makes almost 5 mpg difference overall!  I am compulsive now about getting the best mileage I can because it's possible to see it in real time.  The current trip display is best for me.

The ScanGauge works on any gas or diesel OBDII compliant vehicle.  This means any car sold in the US after 1996 should work fine.  Installation is a snap - just plug it into the diagnostic socket and take a few minutes to set it up.

Check out www.scangauge.com for more information.  I notice they are sold out right now.  I paid $129 for mine and it's saved me a bundle.  I was heading up the grapevine toward LA outside of Bakersfield when I lost most of my power.  By checking the ScanGauge I saw that my MAP (Manifold Air Pressure) reading was low.  Turns out the mechanism that changes the pitch of my turbo vanes had gotten stuck.  I reached in and released it.  There's no other way I could have made that diagnosis without having Vag-Com software, a reader interface, and a laptop computer.

I also got an indication of trouble on my dashboard display that indicated the glowplugs were malfunctioning.  The ScanGauge reported an error code that turned out to be related to a malfunction in the injection pump.  Having that read out at the VW dealer would have cost $80.  Then they would have gotten me for $1800 for a rebuilt injection pump!  As it was I bought an injection pump on eBay for $377 and installed it myself.

The ScanGauge isn't without its flaws but overall I consider it a good value.

I don't imagine most people would use it to the extent that I have, but I think it's worth it just for the MPG display.

In the spirit of full disclosure, I have no financial interest in ScanGauge.

I've suggested that too - it's hard to resist trying for high score!

That's right - and it's okay.  It's not a failure just because some people continue to speed.  

Besides, I think with more awareness, there will be a tipping point of sorts, where the fast suddenly isn't cool any more.

My Saab has this (a '93.. so did the '87... so do the new ones). Both an instantaneous bar graph and a cumulative average. It also has a green economy zone painted on the tachometer and a bright orange "Shift Up" light that comes on when RPMs increase.

I do occasionally see how well I can do, but I can't say I pay attention to it most of the time.

OK then, when you gas up, the pump will transmit the gas price you paid to the engine computer, and then it can display in $ per mile!  If anything will get attention, that will!