This guy at work was saying his car has a computer that tells gas miliage and that when he is coasting down a hill he will drop his automatic honda in neutral.  The computer says he is getting 200 Mpg.
I said your are going to need a new auto transmission if your are going in and out or nuetral and drive all the time.  
    I think it stresses the transmission a little or  a lot...when you plop it back in drive when your done coasting at high speed.

What are your thoughts.. SC

I don't have an automatic transmission, but I shift it into neutral to coast every now and then too. I also don't have a real-time MPG calculator, but I'm sure it would show a similar readout.

Here is something to consider though. If you're coasting in neutral, the engine has to consume a little bit of fuel to keep the engine running at idle speed. In most modern cars with a manual transmission, you can actually use zero fuel if you are coasting in gear. The car's momentum will keep the engine turning and as long as your foot is off the accelerator the engine will cut off the fuel delivery.

Depends on what it is....older cars don't like the whole neutral/ moving shift into drive thing, but newer cars that are electronically controlled will typically know what gear to go into because of inputs regarding engine rpm and road speed.
Regardless, I don't think it would make enough of a difference to do it in the first place.

The automatic actually appreciates the break if you put it in neutral at a light. Takes the stress off the drivetrain, although I don't do it at just every light. I can't imagine it causing any problems otherwise we'd be killing them every time we started/stopped and put the car in park!

You don't want to do this in a moving car, however! That may be what you heard. My Sebring used to register 99MPG (didn't have a 3rd digit) if I lifted in Drive. That's good enough mileage for me without risking my tranny!