One of iOS 4.3 beta, showcased new gestures enabled (like pinch to go to the Home screen), a week lated, Apple said that iPad gestures wouldn't make the cut, and indeed, iOS 4.3 was summarily released without gestures for the iPad and recently-released iPad 2.
It now appears they can be re-enabled by turning your iPad into an iOS developer iPad by using Apple's Xcode developer tools.
To unlock iOS 4.3's gesture controls on your iPad, download and install Xcode 3 (bottom of the page), open Xcode, connect your iPad to your PC, then Window > Organizer and press the "Use for development" button.
You can also download Xcode 3 from elsewhere on the Internet if you don't want to sign up for an Apple ID.
Download: Xcode 3