I never cut off the wrong leg (thankfully!) but I know somebody who replaced the wrong hip. It was a system failure- he raced into the OR and the patient was positioned under drapes and ready to go, but on the wrong side. Boy did he beat himself up and the patient ended up getting both hips done for free. I'm sure this particular surgeon would agree with me that if this happens then "somebody" was negligent. The correct response is a system where "everybody knows" the surgeon will not lift the scalpel unless his/her arrow is visible. That way there is no risk of (for example) offending the scrub nurse by suggesting she has screwed up and got the wrong side, it's just the "system."

As for huge numbers of patients killed: my approach to sensational announcements in healthcare is to ask "why would they say that." If it comes from an organization that is trying to promote a new quality/investigations/whatever system or standard, with a prominent role for themselves of course, then I'd take it with as grain of salt. ;-)