On their What's new in iOS 4.3 page (You need an Apple ID to view link) they wrote:
Test Multi-Touch Gestures for 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. Test them and give us your feedback on the Apple Developer Forums.
I attempted a 4-finger-pinch on an iPod-Touch-4th-Gen development device with the latest 4.3 iOS Beta. Beside of being a very uncomfortable thing to perform on a small screen, I didn't notice anything else happening.