yep, I was just doing some calcs.
If you've got a Hummer H2, you get 10mpg, and like the average American you drive 15,000 miles per year.
So lets say you hypermile the thing and manage to get 11mpg out of it.
That's only a 1mpg improvement, 10%.
But it'll save you over 136 gallons of fuel in one year, that's over $475 here in California.