I just got back from WDW with free dining and have a few observations with the DDP. I liked the plan and with the research I did beforehand (thanks Disboards

) I didn't have a problem. Unfortunaltley, my Mom and DH had trouble understanding the plan. I think they would of had problems understanding the plan even if they read the brochure... It's not as easy as it sounds and there is a true art of how to order something in order to use the appropriate credits that you want. I learned almost too late that my Mom and DH were not using the DDP to the most. I should have given them a lesson earlier on how to use the plan.
My DH and I talked about the DDP later, as to if it was worth it or not since next year we'll be returning not during free dining time. We said that we would still have to buy additional drinks since we liked using the snack credits for snacks, not for water or sodas. But since we really like the character meals and the different TS meals we would get our monies worth from it. You do have to make your ADR's and plan ahead, so if you don't like to be tied down to a schedule, aren't a foodie, or don't eat a lot than the DDP might not be for you.
I like it if it's used correctly and everyone in your party knows how to order and what to use it for.