Don't ask us how they did it, but Apple managed to shave off some weight when they released the iPad2. So don't be surprised if they manage to do that again when releasing the next gen iPad.
The iPad 2 was an already anorexic 600g (Wi-Fi version), and according to Taiwanese suppliers of iPad and Macbook batteries, a new battery pack might even make the next model of the iPad lose more weight. Of course battery life will also be extended, but all that lightweight goodness and more juice also means a higher cost.
For more details, click here.