Others have covered the when and where and how much pretty well. Actually they have left off Palo (adults only restaurant). I understand dinners are very good. Have only done brunch on the 7 night cruises and for us it's a not to be missed meal.
There are 3 main restaurants on board. They serve about 475 people each, twice a night. Palo on the other hand serves about 160 dinners per night - they can take more care in the preparation of the meal (that's not to say that the normal restaurants are poor - they are exellent - just not quite as good as Palo).
A little about the type of food at dinner. There is usually a fish, steak, pork, poultry and vegitarian item done up in a very special way. They also have "plain" fish, steak, pork, poultry available. The food generaly is rich and very tasty.
This IS the time to be brave and adventurous. I generally don't eat fish (salmon excepted). I was brave a couple of times and tried their fish (grouper

I remember the other I don't) The grouper was great and the other was probably the best meal I have ever had!!

If you order something you end up not liking, don't hesitate to ask for something else. They will bring it out to you in a very short time. On lobster night ("Captian's Gala") several men at our table ordered the steak dinner and the lobster dinner (surprisingly they didn't offer the "Surf and Turf" as a menu option

)
Same goes for any of the courses - order as many as you want. Your table can order an appitizer or two to share, then everyone orders their own too (or everyone order two - whatever)
As far as the courses go they are: Appitizer, Soup/Salad, Entree, Dessert. There is always bread avaiable (each restaurant/menu has a bread special - they make their own bread - the crousants are the BEST).
Many of the servers are great. If for example you mention that you love Creame Brullee', your server may just bring you one even if you order something else (and even if you are not in Lumiers), they may bring you one every night, may ask if he can bring you one. Don't be surprised. Maybe Rae will share her Creame Brullee story.
Enjoy the experience!
Don't worry about wasting food (my family has a real problem about wasting food).
DCL recycles it (see tomorrows lunch

-- no NOT really at lunch). They turn it into fish food and overboard it goes.
The biggest tip: Forget the elevators, take the stairs. After two days on board, really cut back on the amount you eat at lunch. We usually skip it - and will pick up some fruit from scoops in the afternoon.