1) The Dining Plan is not nearly the moneysaver it used to be. Some guests can do better paying out of pocket, depending on what they like to order and where they like to eat. For example, a party that prefers a la carte restaurants to buffets, drinks water and rarely orders dessert can spend less than the cost of the dining plan.
2) If you don't eat or order the way the dining plan works, it isn't really worth using. If you like ordering a couple of appetizers rather than an entree, or your preferred drink with a meal is water and/or an alcoholic beverage, it's probably not going to work well for you.
3) If you prefer not to eat as much food as prepaying for the dining plan buys you, then it's likely not a good purchase (if you tend to split meals or eat mostly at CS to give yourself more park time), although a lot of guests purchase the dining plan so they can feel as though they are "splurging" and getting snacks or desserts they ordinarily wouldn't get, for example.
4) Disney rather counts on guests being unable to use all their prepurchased credits. When this happens, Mickey gets to keep the money already paid for food that wasn't even ordered. Many guests make plans to use every credit, but a lot of guests don't plan (possibly they buy the dining without knowing they ought to plan their meals), or the prepayment aspect is what matters to them and they don't care if they leave credits unused. You can possibly get a deal out of the dining plan these days but you need to make plans to do so.
5) Not everybody wants to make a restaurant reservation for every day of their vacation. And now, there are 23 restaurants and one special Fantasmic package that require a credit card hold, a no show fee and cancellation a full day in advance, so you can't back out at the last minute if you don't feel like eating, without it costing you.
Now, the plan is like $46-47 a day
2012 adult price for the regular dining plan in non-peak season is between $51 and $52 per night.
I realize this thread was moved here - I removed a sentence from a post where someone stated exactly what they planned on tipping, because tipping preferences and habits are not up for discussion on the Restaurant boards. Anyone with questions about tipping discussion should see the Tipping Information sticky thread on the main Restaurants board.