With the dining plan, you are basically just given a big pile of meal credits when you check in. So, for 3 nights, you will get the 3 counter service, 3 sit down meals and the 3 snacks for each person. If you want to use them all the first day, you can do that. If you saved up all your snacks until the last day, you can have a meal of Coke and popcorn. Just depends on how you want to use them.
The only DTD restaurants (sit down) is Cap'n Jacks, Planet Hollywood and Wolfgang Puck's Cafe. For the last two, you can only order certain items. The Swan and Dolphin are not Disney resorts, so nothing there is included. Oh, and 'Ohana is on the list. You can see the entire list here, and what is included:
http://www.disneycentral.com/images/diningplan.pdf