I wish I'd thought of this for my job listings, it's a fun couple minutes. Well done, gentlemen.

So many of these puzzle challenges (e.g. Google Aptitude Test circa 2004, Facebook Programming Puzzles, etc) seem like they would discourage people who already have a great full time job, or actively maintain an open source project, etc... who are exactly the people you want. This one seems to strike a great balance between time invested and skills/thought process tested.