I'm always impressed at my primary care doc's breadth of knowledge. Whatever the topic (knee injury, heart rate, asthma...), he has working knowledge at easy recall, which he augments by consulting electronic reference materials during appointments—all while staying engaged with the patient (me). This is all in the context of a standard physical, and often the subjects (such as the knee injury) haven't been mentioned beforehand.

I do think he's in the top 5% of MDs, so of course we can't expect this of everyone. And specialists obviously specialize. But there is a large segment of the profession that requires a wide breadth of knowledge in a domain that frequently changes.