There was a contestant who appeared not long after it became a regular series, and I only remember vague details here. IIRC, it was Rudy Reber, and got a question about who a movie director who directed a Michael Jackson video. His PAF was very confident about it being (I think) John Landis, and it was not. The question was for $125 or $250K, and he went home with 32K.
(Googles) It was Rudy Reber, but he played for 500K, and the question asked who directed the Bad video. Reber went with his friend's answer of Landis, but it was Martin Scorsese.
As far as Kati Knudsen, I'd seen quite a few stories about how difficult of a contestant she was, from the studio all the way to the cab ride back to the airport.