The Global Mundo Tapas restaurant recently replaced its' menus with iPads. This allows customers to browse the entire virtual menu and see pictures of the food as well as get recommendations for complementary wine.
The iPad sends the order back to the kitchen and the back end database keeps track of stock as well so if something is sold out it automatically gets removed from the menu.
This is just the beginning. In the near future I can see the tablet devices replacing paper forms that are filled out in places municipal and doctor's offices.
Source w/ Video: Restaurant Replaces Menus with iPads