In general practice, you will find that doctors become less accurate as they get older; whereas in surgery, older doctors generally perform better with less complications. The reason is that the feedback loop in surgery is instant -- you do something wrong, you have to fix immediately -- wheas in general practice, it is often the case that the doctor never even knows of the prescribed treatment worked so the feedback is a lot "weaker". Therefore, I think Watson could be hugely beneficial and counter-balance the biases and decline in skills that plagues many doctors who work in general practice.