He didn't guess any in 20 so far, but he actually got close for some reasonably obscure characters (Duncan Idaho (guessed Paul), Mr. Darcy, Vinton Cerf (not really obscure), etc.).
He completely failed at Otto Jespersen and Ötzi the Iceman, though.
20 questions is actually a pretty interesting and powerful piece of information theory.
The worst part is, they're probably not even selling the information they're collecting.
Actually, why isn't Google running 20 questions games? They should be running lots of them. Guess any person. Guess any website. Guess any location, or book or movie, etc. They're not hard to set up, and I bet they could collect even more information than from that picture labeling game.