I've stumped it once before, but I can't for the life of me recall with who.
It just got Starbuck from BSG, which isn't a difficult feat in and of itself... But it seriously only asked three questions where the answer wasn't an outright no. How the heck could it know it was Starbuck from it being female, blonde and a TV actress? Sure every ruled out question narrows the possibility... but still, wow.
Oooh, stumped it with Mokoena from Brink. Original guess was someone from MGS, but he got it right the second attempt. Consider me floored.