I would never consider paying for FPO unless the discounts were much better (and after factoring in the tax) and only if I had the ability to return the car with no gas.

I think the more interesting question regarding fuel is when to accept the free fuel PC coupon over say a $20 off PC coupon. When I go for the free gas based upon my anticipated mileage, I always pray for a car with a gas tank that can get close to 400 miles or better with highway mpg. Then I return the car just below the E level or substantially lower than E if the fuel gauge E is obviously too high.