Articles from the IBM Research blog about how Watson works:

• Watson’s wagering strategies
• Knowing what it knows: selected nuances of Watson's strategy
• How Watson “sees,” “hears,” and “speaks” to play Jeopardy!
• An inside look at the Power behind IBM Watson
• IBM computer system a scientific achievement in natural language processing

A Nova episode on Watson, entitled "Smartest Machine on Earth"

A technical article in AI Magazine describing in detail how Watson works.

An article describing "the Basement Baseline" that IBM commissioned to be sure they wouldn't be beat by some upstart hacker in a basement.

A spreadsheet of raw data on Watson's performance.

Other stuff, including actual video of the episodes should be appearing at ibmwatson.com. Some intersting stuff that's there now:

• What is Toronto???? explaining Watson's final Jeopardy answer in the first game.

There's lots of news coverage, but this is the stuff that I'm aware of that's most interesting to people in the NLP field (like me) or close to it.