This photo - not very exiting I know - is the result of a experiment shooting tethered using the app DSLRemote Pro for iPad.
My MacBook is connected to a WiFi and so is the iPad. The Nikon D300 is connected to the MacBook through the normal USB-cable that follows the camera. So it is a really easy setup. The app DSLRemote Pro also need a client to be installed on the MacBook (get it from the developers home page), that will set-up your MacBook as a "server" (harmless). Start the DSLRemote Pro app on the iPad and as soon as it has found the "server" and connected to the camera through the "server" you can control the D300 through the use of various controls on the iPad.
It worker flawless for me and as you can see from the photo, I managed to "shoot" a pigeon. The autofocus function works by putting your point finger on the "release" bottom on the iPad screen and hold it there while the AF is working. Releasing your finger will take the shot.
Here is my set-up :-)