We've used the DDP twice before (once free) and will be using it again in a few weeks. We love it. I find it very easy to use and the only minor trouble we've ever had with it was when the CM didn't know his/her hiney from adam. A CM at Akershus charged our 2yo a TS meal, then it took lots of wrangling(at POR) to get it back(another person who didn't know her hiney from adam

). The server at San Angel Inn could barely speak English and was absolutely clueless. These situations were all in the first year of the DP. We had no problems last year.
You can still find some discrepencies and differing "opinions" out there as far as CM's, restaurants, etc. but with that you just roll with it. For example, one restaurant might allow a smoothie as your drink while another one won't. The same goes with servers.
As far as us, we are well versed in the DP, and we have no problems with it. Snacks can be the most confusing, but most places have the DP insignia next to the item if you can use a snack credit for it. Easy Peasy.