Discover card is ending a 5% off on gas today - but starting another 3 month period July - Sept. Believe me, that 5% is a lot with the gas prices what they are now. I made sure to fill the tank yesterday. And I'll be sure to use my Discover card for the trip back from Alaska. Probably will continue using it for the lower percentage now - but definitely then.
For those who think using a credit card is hard, because then the money isn't saved, you can always pay it as you use it - or put aside the money somewhere each time you get gas. It doesn't do any good if you carry a balance - that will take that 5% away quickly.