It was definately worth it. We were there from 8/13- 8/19. We ate at Coral Reef on 8/13 & 8/18. Sun. our reservation was @ 4:20. We arrived at 4:10 and we were seated by 4:20. On Friday we had 4:30 res. We got there at about 4:25 and we were seated by 4:40. We were a party of 7.
Regarding system being down: One time we went to purchase a soda at snack cart who told us the system was down, but would be up soon. We walked until we came to the next cart and the system was up - The problem must have been sporatic throughout the day - because, although we heard people talk about the problem, we never had any other trouble.
As far as the tip - According to another board - In any restaurant (disney or other) the tips are "shared" with other workers in rest. (Not sure exactly who, but bus boys, prep people etc...) This leaves the server with about 10% - I am sure that they didn't get a flat amount where we ate because the encourged you to pick the most expensive meals. At Coral Reef our waiter even tried to "suggest" we get the fried scallops on the ceasar salad. He clearly was trying to increase his tip.
We had great service at Coral Reef, Le Cellier, Planet Hollywood, Hollywood & Vine, and Biergarten. If any of them didn't ask up front if we had the dining plan, we told them - and that helped things go smothly. Any small inconveniences caused on dining plan are FAR outweighed by the benefits of savings and convenience that you get