[ProblemFactory]

I would expect that Watson is used as a discovery, not a decision tool - something to point out the symptoms as matching an uncommon disease that the doctor had not otherwise considered.

There are around 500 000 biology and medical research papers published per year (http://www.stm-assoc.org/2012_12_11_STM_Report_2012.pdf), and it's completely impossible for a doctor to keep up with all of the latest knowledge. A search engine can help a lot in discovering otherwise unnoticed connections.

I'm not sure how insurance companies are going to approach this - but "the computer agrees with my decision" seems to be a good defense argument in a malpractice case. And if the end result is statistically better, then insurance companies will adjust their prices.