I have stopped doing puzzles for companies because I had the same experience everytime I solved a puzzle on a companies website. Common courtesy dictates that if you have a problem on your site that would take more than a couple of hours to solve then you should at least bother to reply personally when a candidate solves the problem (I am looking at you Quora). At first I thought it was just because my solution and resume got lost in the stack of applicants so I contacted someone at Quora on thier direct email address. Still no response.