You might find more info on this on the dining board, but the short answer to your question is yes, the dining plan is a great deal.
However, there are lots of things to factor into the equation as to whether its right for you. If you guys are foodie, like my girlfriend and I, then the DDP is worth every penny. Every night, you get to try a new resturant, get your own appetizers, desserts, and the work. You get to try so much food, for us, that's more exciting than the parks themselves. Also, I did some figuring, and if you were to pay for all the food you get on the DDP, it comes to about an average of $82 a day. Considering you get all of that for just $38 a day, its a great savings.
But, you just have to decide if all that food is right for you. You can easily eat two counter service meals a day and get by on about $25 a person, a day.