Belatedly, because the neighbor's WiFi's down:
I was Gatekeeper and I agree with this post.
I approached the experiment as a game - a battle of wits for bragging rights. This turned out to be the wrong perspective entirely. The vulnerability Tuxedage exploited was well-known to me, but I never expected it to be relevant and thus didn't prepare for it.
It was emotionally wrecking (though probably worse for Tuxedage than for me) and I don't think I'll play Gatekeeper again, at least not anytime soon.
Update 2013-09-05.
I have since played two more AI box experiments after this one, winning both.
Update 2013-12-30:
I have lost two more AI box experiments, and won two more. Current Record is 3 Wins, 3 Losses.