In my harsh tablet battery test, where I play a constant loop of video with the screen set to 75 % brightness and Wi-Fi on to retrieve email in the background, I got almost exactly five hours, which is Asus's official battery life estimate.
The same device could also play video that is streamed over an airport network and could, in theory, surf the Web and retrieve e-mail easily, with all the heavy lifting done by the Powermac or iMac it's connected to.