Okay, basically the DDE is a discount program available to FL residents at an annual cost of $60 (less discounts one may receive as an annual pass holder or a Disney club member). There are several benefits available to a subscriber. They are detailed
here
It sure sounds like a pretty good program if you dine at WDW (even occassionally) because it certainly wouldn't take you long to earn back the cost of the card with the 20% discount and free parking you'd receive.