Gizmodo:
How to Activate the Best Secret Feature In Your iPad
Your new iPad—and old too, with iOS 4.3—has a new hidden feature that Apple doesn't want you to know about: Extra multi-touch gestures that completely changes the iPad experience—for the best.
New iPad hidden gestures
• Swipe four or five fingers—to the left or to the right—to navigate through open applications.
• Swipe four fingers up to access the running apps tray and playback buttons, including Airplay controls.
• Pinch with all your fingers to go to the home screen from any app, without touching your home button.
For example: With a simple hand swipe, to the left or right, you will be able to navigate through running applications. Once you try it, you won't be able to go back.
Sadly, Apple doesn't want you to use these features yet. They could have included the switch in the general preferences for everyone, but right now this is only available for developers, so they can give feedback.
It will "only" cost you $5
The good news is that you can activate them and it's really easy: It only takes one click. The bad news is that you have to pay an extra $5 for Xcode 4, in the Mac OS X App Store.
Here's how to do it:
Gizmodo, the Gadget Guide