I've booked the counter service plan. We're doing a 7 day trip, and I don't want to spend a lot of time in sit-downs. I looked at our receipts from our 2007 trip (where we had the basic plan, but wrote down our totals on our receipts before we signed them), and we averaged $45-55 per counter service meal. $15-20 per snack. Using those figures, we'd come out even using the CS plan. However, if we were paying OOP, we proably wouldn't mess with a dessert at every meal, meaning we'd save a little bit paying OOP. (I guess I should add here that we're 4 adults -- my dh and I, my 15 year old son and 13 year old daughter, plus one 9 year old daughter.) However, if I switch to paying OOP, I know I'll be tempted to book a couple of TS meals, which would then add to our food costs.
I know the basic plan is not cost-effective for us, so we'll either stick with the CS plan or go OOP.