Just returned from Disney. Used mostly gift cards this trip. I bought them for exactly the same reasons - gas savings!
No problem using them. They do not expire (according to Disney).
When I paid off my room ressies on line, I entered the gift card numbers. Only one worked, so I had to call the rest in. No problems. A CM handled it.
Word of warning, if you pay in full by credit card, apparently Disney won't credit back the reservation charges to your credit card at check out time (this is what I have been told). So, if you are intending to pay for your reservation with gift cards, you have pay for a up front with the gift cards.
It was very easy to use gift cards for restaurants, tips and purchases. When you get your "Key to the World" (room key) card the CM will ask if you would like to pay for purchases with it. They then link it to a credit card. You can go to the front desk either the night before or the morning of check-out (before 11:00 am) and have your charges to your credit card "reversed" and pay the balance by gift card.
I just asked the CM at the front desk what was the easiest way to handle it and she told me the above.
On a previous trip we applied some of the gift cards to our account prior to charging anything, so we had a credit on the account. That CM seemed to prefer to handle it that way.
DO NOT throw away the gift cards until the account is settled up. If they need to put some funds back on your card, you have to still have to physically have the card. They cannot put funds on to a different card.
Hope that is clear.
