In his post-match article we find this interesting bit about how Watson ended up using a physical buzzer -- much like the one used by human contestants:
It was the second night of the Man vs Machine Jeopardy match that the Sony nightmare appeared to be coming true. Throughout all of the negotiations between IBM and Jeopardy!, a division of Sony Pictures Entertainment, each side had been obsessed with its own disaster scenario. IBM, of course, worried that its computer, Watson, would lose and look foolish, embarrassing the company and the team. Jeopardy, meanwhile, worried that Watson would grow too smart and too fast, and steamroll the human competition. This would be demoralizing and, worse, bad entertainment.
It was this concern that led Jeopardy to press IBM, only nine months before the match, to fashion a finger for Watson, so that it could physically press the buzzer. Previously, Watson had been buzzing electronically. IBM’s chief scientist, David Ferrucci, initially objected to the finger. “They’re trying to graft human limitations onto the machine,” he told me one day over lunch. This would slow down Watson’s buzzing by perhaps 8 milliseconds. He worried that Jeopardy might continue to ask for adjustments in their hunt for a fair and exciting match. [...]
There are also other bits -- especially about the second episode in which Watson demolished its opponents and produced an Epic Fail moment of its own at the end. So, go read the whole thing.