I booked the 2008 dining plan
I don't know who broke it down on the DIS or how they did it, but here are my own un-scientific findings based on the allears.net menus...
We would do 1 TS everyday regardless of whether we get the DDP so that isn't a factor, and would also do 1 CS and bring granola bars or the like for breakfast in the room, so the DDP really fits our family. I figured out "what it should cost" for our upcoming trip using the following notes regarding sharing, etc. -- all figures include tax & tip:
Ohana -- 3 Disney adults & 1 child $112 {family style, still get appys, drinks & desserts)
Electric Umbrella -- 3 combos, 1 kids meal, no desserts $34
San Angel Inn -- 2 combos, 1 kids meal, 1 appy, 1 dessert, 1 beverage $91
Flametree BBQ -- 2 plates, 1 fries or rings, 4 drinks, no desserts $32
Boma -- 3 Disney adults & 1 child $105 {buffet, still get appys, drinks & desserts}
Pecos Bills -- 3 combos, 1 kids meal, 4 beverages, no desserts $36
WCC -- 3 skillets, 1 kids meal, 2 desserts, no beverages $104 {salad & cornbread part of skillet}
Pizza Planet -- 2 combo meals w/salad, 2 indiv pizzas, 3 beverages, no dessert $35
and a total of 8 snacks for 4 of us to share over the the 4 days $25
Total: ~$574
The DDP plus tips will cost us ~$546 for 3 disney adults and 1 child, so we are still saving around $28 without having to scrimp, share, worry about prices, or deny anyone desserts. And that $28 can be used for a couple of appetizers at San Angel Inn or something else at WCC if we really need the extra food.
Hope this helps someone!