Preview at WWDC likely in June, followed by September launch.
Video of New Multi-Touch Gestures on iPad iOS 4.3
One of the most interesting new features found in the developer release of iOS 4.3 is the introduction of four and five finger gestures for the iPad.
This beta release contains a preview of new Multi-Touch gestures for iPad. You can use four or five fingers to pinch to the Home Screen; swipe up to reveal the multitasking bar; and swipe left or right between apps. We are providing this preview before releasing them to the public to understand how these gestures work with your apps.The above video shows the user four-finger swiping from left/right to switch between multitasking apps. Meanwhile pinching with 4 or 5 fingers can return you to the home screen, which potentially removes the need for a physical home button.
iOS 4.3 is not yet available for public download.