Disney's free dining offer begins August 16th and runs through October 1. If you're taking advantage of this time to visit, make sure you make advanced reservations for the restaurants for your table service meals. You can make those reservations 90 days from your arrival day by calling 407-WDW-DINE. You may also want to have a time range in mind so if the time you wanted isn't available, you can check a little earlier or later. You can also schedule your table service meal at lunch if you choose.
Also, let them know if you are celebrating a birthday, anniversary or anything else you may be celebrating.
We had this nice happy anniversary dessert brought to us after our dinner at the California Grill. Disney goes over and above this year when you are celebrating because their promotion for the year is "What Will You Celebrate?"
Some restaurants will require a credit card to hold the reservation and they have a cancelation policy that charges your credit card if you don't show or cancel within the time period required. This is currently done at some of the more popular restaurants so that people don't double book reservations and not show up for one.
I would always recommend trying the table service dining plan at least once. It's a lot of food but it's a great way to experience some really fine dining.