Multitasking gestures were earlier spotted on iOS 4.3 beta 1 which were unpredictably removed from the next beta and so from the public release. It seems that Apple enabled those MT gestures just to test it for future use, may be iOS 5.0. Those who missed them can get it enabled on their JailBroken devices (only iPhone 4 and iPodTouch 4) through a tweak by¬†cookie181992 .
After the installation, apply through winterboard and a new toggle will automatically appears in settings application. These gestures lets you use four or five fingers for pinch to home screen, swipe up to reveal the multitasking bar or swipe left or right between applications.
You can download MT gestures from the ModMyi Cydia repository.