even if you don't make super advance reservations you can still usually get into most of the restaurants you want by just reserving a day or two in advance....
however, for something like Cinderella's breakfast in the castle, you do need to make the reservation way in advance...also for preferred times in any of the restaurants...
but i wouldn't freak out over it the way some people do....if you're flexible in your times, you can get into most restaurants with just a few days notice...unless you're going during christmas/new years/easter...
but any other time..
however since you don't have to put down a deposit (except for Cinderellas) you can go ahead and make a ton of reservations even if you're not entirely sure of your schedule.....and then once you have your schedule more firmed up you can change things accordingly...