I thought I was staunchly in the DDP camp after our anniversary trip in February of 2010. We did the deluxe plan, btw. My husband and I had either breakfast or lunch somewhere and then we hit a signature nearly every night. It was great and we really liked not thinking about prices at all. That said, I often have zero interest in eating dessert immediately after my big meal, but we ordered them anyway.
We went back this past February, this time with our three year old son. Because of the amount of character dining I had planned, we did the DxDP again, as I could not see the wisdom of doing the DDP and still paying OOP for a few meals. My husband and I quickly realized we had made a HUGE mistake. For one thing, travelling with a three year old demands a certain amount of flexibility, something you cannot have if you want to get your money's worth out of either dining plan.
We were also underwhelmed by a number of the 1 credit TS places we ate at and I wondered if we wouldn't have been better off with just CS or snacks.
As a TDC Nala said, there are a number of places where I'd rather have two appetizers, or an app and a salad, forgo my entrée entirely, and not order dessert. We also don't need three TS meals per day. We barely need two!

We also left more credits on the table than I cared to count.
And again...if you're planning on doing a ton of signatures and really want to order all three courses, deluxe is probably a good deal. I'm sure if you have more than one kid, free dining is an awesome deal. And I could see returning to the DxDDP if my son becomes one of those adoloscent boys with a bottomless pit for a stomach.
Sorry for the long post, but I've thought about this a lot since our last trip and this is why we're forgoing any dining plan for our upcoming trip.