I'm slightly OCD when it comes to dining plans so i'll give it a shot
The dining plan has been better value (they changed it for 2008 and removed the inclusion of 18% gratuity and appetiser at the table service meal) and is not necessarily a good deal if:
1. You are an annual pass holder. If you have an annual pass a DDE card may be better value as you get a discount of 20% at over 70 restaurants at Disney (the discount applies to alcohol as well). They will now add an automatic 18% gratuity but that seems the acceptable tipping level in the US anyway so you're still getting 20% off food and drink. Great value if you prefer sit down restaurants to the counter-service ones and you like to have drinks with your meal.
2. You don't like to waste your time in sit down restaurants and prefer to only eat a sit down meal 2-3 times a week.
3. You eat off-site a lot. If you have a lot of off-site favourites you want to go to then again the dining plan isn't such a great deal as you can get great value off-site at places like Ponderosa, Golden Corral, Applebee's, TGI's etc.
4. If you are going with kids between ages 3-9 they HAVE to order off the kids menu on the dining plan. From what i've seen of the kids menus I can safely say neither of my nieces would be that enthused by what is offered as they are used to eating what their parents eat and probably have never eaten a chicken strip in their lives

Not a problem if you do lots of buffets but can be a bit limiting for chlidren used to eating a more varied diet.
If however you are going to be eating mostly on-site, want a sit down meal every day then I think you'll save the stated '30%' that Disney suggests by buying the dining plan. And its nice to be able to order anything from the menu without worring about price. The dining plan can be VERY good value at restaurants like Coral Reef, Tutto Italia, Le Cellier, Kona Cafe etc, all very good places btw
We are purchasing it for our trip in January because we will be eating mostly onsite and we're staying at Deluxes so that if our baby girl needs to go back to her room/is being fussy we can just eat at our hotel or order room service (which is worth 2 dining credits) so we're not stuck eating toasted bagels at night hoping she'll fall asleep
If you go to the main website of this forum,
www.wdwinfo.com the dining section lists all the restaurants and menus, hope this helps
