He is so far unstoppable. He is very quick with the buzzer and has superior knowledge. His strategy is not based on choosing questions by subject matter. He actively searches for daily doubles. If he misses those, he has at least deprived the others of them. Last count, 27 wins.
His Daily Double strategy definitely seems to be paying off. It will be interesting to see whether someone can eventually slow him down by controlling the board earlier in the game.