How to make use of the entire screen area on Android 4.1 in full-screen mode? The system bar (aka notification bar) on my new tablet (ASUS Transformer Pad) is always visible, even when watching YouTube "full-screen".

The amount of space wasted is not insignificant, especially when watching a 4:3 video. Is there any way to reclaim it and watch videos/play games in real full-screen?
It is not intended to hide the system bar (combined soft button/notification bar) on tablets. Imagine the bar is hidden and the app you are currently using does not offer an option to exit. -> Your are stuck within this app.

Some custom ROMs offer the option to hide the bar.

General option would be to use some third-party-apps like Hide Bottom Bar or full!screen which can disable the bar somehow. Unfortunately these apps require root.