I've never done the regular DDP, but I don't think it's really for me. I'm totally sold to the QS: doing it for the third time in August.
I like being free to eat when I want and to not eat when I'm not hungry. On our first 7-day trip in May 2009, we had 2 ADRs for which we paid OOP. In order to get the two restaurants we wanted with decent hours, we had both ADRs in the same day (Sci-Fi Dine-in for lunch and San Angel Inn for dinner). On our lunch ADR, it was so hot and humid, I was barely hungry, and just ordered two appetizers (chili and salad). Had we not had that ADR, we probably would have eaten lunch an hour or more later, and would have split a QS meal.
On our second 7-day trip on the QS plan last December, we only had one ADR (Boma), and again, I didn't like having to plan my whole day around that one meal.
In August, we're on a budget trip, so the credit card stays in the hotel safe, and we're sticking to the plan, not buying anything OOP (except lockers at the water parks). From our past two experiences, we know that for two adults, especially in the heat, 28 QS meals and 28 snacks for 7 nights/8 days is way enough.
We're planning a trip with my parents in May 2011 (their first visit!). Since they are getting older, don't eat that much and won't want to walk as much as we do, we may try the regular DDP (if we get a code or good deal, and depending on what pans out regarding the possible changes discussed in other threads), or simply go OOP for the whole trip.