I would suggest, if you can, check the ADR mobile site while in the parks. It's a really fast and super easy way to check last minute reservations.
A few weeks ago we were on a short notice trip and had made no reservations. We were in a gift shop in Adventureland and my wife asked where are we going for lunch, Cosmic Rays or Pecos Bill (which are both really good). Anywhoo...I checked the mobile ADR site, around 11:30a on my iphone and looked for "Lunch, Magic Kingdom" it came back with most of the table restaurants in MK having space available and a Crystal Palace reservation for 2pm. We haven't been able to get in there for a while so we jumped at that and had a great time. Tigger was in rare form that day!
If you have an iphone or any phone that can get internet you can log onto the mobile version of the ADR website.
Make this a bookmark if you do:
disneyworld.disney.go.com/reservations/dining/m/
I hope this helps!