In my experience the installation of a chip increases gas mileage, not decreases it. Only your right foot may cause a decrease in mileage.
We have some of the cheapest gas in the world anyway. Compare to Asia or Europe. Even if the chip were to cause a 10-15% decrease in mileage, that would equate to only a couple hundred dollars a year versus about 15,000 miles and 300 - 500 HOURS of driving enjoyment.
Finally, if paying $3.00 or $4.00 a gallon for preimum would help get the gas hog SUV's and pickups etc off the road, count me in.
Mike Holbrook
Meridian, Idaho
1992 535im, 17", Euro M5 Throwing Stars 8's & 9's, FK-451 235/45s & 255/40s, M5 Sway Bars 25/20, Conforti chip, Lowes Ram Air, glass sunroof