Time Stop feature.
It's not my idea, and I am not the first to implement this, but what amazed me really is the fact that it required only 3 lines of code to be implemented <!-- s:) --><img src="{SMILIES_PATH}/icon_smile.gif" alt=":)" title="Smile" /><!-- s:) --> and 3-4 lines to make it toggle on 'impulse' command (in this demo it was bound to some key):
<!-- m --><a class="postlink" href="http://www.youtube.com/watch?v=nOQiInSZo6Q">http://www.youtube.com/watch?v=nOQiInSZo6Q</a><!-- m -->