Very cool. My only concern is if you have a screen with a lower resolution (1366 X 768), the drawer with the source code causes the user controls to be hidden, so it's not immediately obvious that those controls exist.
Same goes for if you have a bigger screen but don't maximize your browser.
Windows has terrible virtual desktop support; as a result, I don't usually scale windows to full screen so I can actually keep multiple windows straight. One of my big pet peeves is when websites don't scale well to smaller width or height (height seems to be particularly neglected by web developers).
