YouTube offers many other useful shortcuts:
* left/right arrow - seek backward/forward 5 seconds
* ctrl+left/ctrl+right - seek backward/forward 10%
* home/end - seek to the beginning/last seconds of the video
* spacebar - play/pause when the seek bar is selected
Here's a video you can use to try the shortcuts (make sure that the seek bar has focus by clicking on the small play button):
{ via The Next Web. Thanks, Kevin. }