DH and I were on the Premium plan last August. We loved it! Granted, we didn't take anywhere near full advantage of all the other extras the plan includes (We did 1 tour, and went to Cirque, but that was about it for the extras) so Disney definately came out ahead on that end of the deal. But as for the dining part, we did some damage, let me tell you!
Breakfast, lunch and dinner, just about anywhere (no room service, no V&A and nothing at Swan/Dolphin). Unlike the regular
DDP, you don't have to worry about counting TS or CS (and no snacks included either). You get three meal credits per day (or is it night, I can't remember). They are not designated by type of meal, so you can use them whenever while you are there. And you get the same for each meal as you would for the TS credit on the regular plan. So, for an example, we ate at Chef Mickey for breakfast (full buffet plus drink), Crystal Palace for lunch (full buffet plus drink) and California Grill for dinner (app., entree, dessert and non alcohol drink)...all in one day. Another day we did the buffet at Trail's End for breakfast, Le Cellier (I think that's the name) for lunch after a tour, and then Citricos for dinner before heading out to Cirque (that was a really long day!). You can use the credits at CS places if you want, just as you would a CS credit on the regular plan. And you can use them at the Sig. places. The difference being that each place only subtracts 1 credit from your plan (not 2 for the Sig. places like on DDP). Just be sure you tell the server that you are on the Premium plan, I guess it has to be entered differently.
I will admit that it is a LOT of food! Especially if you are doing all sit down/TS type places, three times a day. And it takes a bit of extra time to eat that way. But we planned that trip around the food. The credits that we didn't use for ourselves, we just put toward treating my dad and step-mom to a couple of meals at the end of our trip when they came to visit us. The plan is a great way to try a bunch of different foods or restaurants that you normally wouldn't do, and you are not limited to having to do CS if you don't want to (we are not big CS fans, nothing wrong with them, but we prefer to have nice sit down meals instead). And no counting/saving credits in order to eat at the nicer places. You can even do the dinner shows for only one credit used.