The iPad is a pretty awesome device to use to watch movies, play games, manage your calendar, and do a whole lot more. It does have a beautiful display, so it is not surprising to see people want to use it as an extra display for their computer. Duet Display makes that happen. It lets you pair your iPad (or iPhone) with your Mac to become more productive. It offers you a lag-free experience and has a plug and play setup.
Duet is pretty easy to use. You just have to download the app to your Mac and iOS and connect your iDevice to your Mac. iOS devices running iOS 5.1.1 and later are supported. Early users have complained about bugs, but the idea sounds quite intriguing. You can find this app on the App Store.