We chose to try the dining plan one year b/c we wanted to try the food and atmosphere of all the highly recommended restaurants Disney had to offer. Because it was not cheap, we felt we had to get our money's worth and used every CS, TS, and snack credit we had. We felt disgusting every day with the amount of food we received and either ate (physically ill feeling) or wasted (emotianally ill).
Also, we felt our trip was consumed with making our reservation time which, since they have to be booked so far in advance, was very often inconvenient considering our current activities or appetite at that time or on that day.
The next year, I decided to keep our food and snack receipts and compare them to what a dining plan would've cost us. Doing our own thing saved us money. It was not a tremendous amount of savings, but it was much more convenient to tour and eat OUR way on OUR terms.
Our preference in eating is mostly CS and snacks and the occasional TS to our favorite restaurant, Le Cellier (that was the only restaurant out of all we've tried that we felt was worth the money; if DD was still young enough, I would also do the Akershus Princess breakfast). Granted, we did not eat at fanch shmancy TS's all week (just once or twice), but that's not how we want to spend our park time anyway--worrying about when our next reservation is, wasting an hour to hour and a half eating, feeling guilty about not using up all credits or feeling guilty wasting food we were just to full to eat another bite of.
From now on, we will stick with our own dining plan--eating whenever, wherever, and whatever we want. The planning aspect and the overwhelming amount of food is just not worth it for us. And, quite honestly in our opinion, very few of the Disney restaurants live up to the hype so if there are any others we'd like to try in the future (like O'hana), we will be paying out of pocket for them.
Good luck with your decision, I know it's a tough one to make the first time!