We did the basic plan in May 2007 and really liked the fact that most everything was paid for in advance. At that time, the appetizer and tip was included, and I don't think we paid for any meal out of pocket. We spaced the meals out so that 2 a day was enough, and filled in with snacks and breakfast in our room. The only thing we did not like about it, was having to be very scheduled. There were a couple of occasions where the kids were like 'it's time to eat AGAIN???' There was even 1 or 2 days where we were not even hungry at our ADR time, but still went to 'get our money's worth'.
For our May 09 trip, we have chosen the QSDP, mainly because of the schedule thing. QS works great for us, and there are many great options that we found last time, such as Wolfgang Puck Express. We are doing 4 TS meals OOP during our 8 night stay, which is plenty for us. The other great thing is that we get our refillable mug, and plan to use our meal included drink for water, so there is less we have to bring with us and less to lug around in our backpack. We think our credits will last us all week, b/c we will do some sharing. We won't have to bring a bunch of breakfast stuff, and we get 2 snacks a day on the plan, so won't have to bring a bunch of snack stuff either.
All in all, we like having as much as possible pre-paid, then we can order what we like and not think about the cost.