It's pretty cool, but I figure, if I have to spend 5 minutes and drive an extra round trip of even just 5 miles, it makes no sense to save 10 cents a gallon even. If put 10 gallons in my car, that's one dollar "saved", but with 20mpg, I spent 1/4 of a gallon getting there, which is about one dollar when gas is $4 a gallon. So my net gain is zero, minus the time to drive and the wear of stop and go on the car. I figure cost of driving per mile inclusive of all costs is about 40 cents.