On day 2, Watson comprehensively outscored his human opponents.
To some extent, it seems Watson is at an advantage because his pneumatic button-pressing system can react faster than any human possibly could. This severely affected Ken Jennings, who obviously had some of the answers and showed frustration at never being able to get to the buzzer first, shaking his head on occasion.
Perhaps a more fair way to assess Watson’s intelligence (as opposed to his button pushing prowess) is to adjust Watson’s button presser to be more commensurate with the pressing rate of human nerve systems.
Although Watson is doing great, it is becoming more apparent that Watson doesn’t understand the nuances of language in the clues as well as a human could. There’s a document here (PDF) detailing some of Watson’s programming.