@Bozostein (I'm not in the physics field, so I'm not too sure): I doubt it. Physics.SE doesn't look well-known to me; though SO certainly is.
On a related note, I have heard of interviewers being impressed by Wikipedia adminship. Wikipedia is a tool used by almost everyone, so saying "I'm a WP admin" has a much better impact than saying "I'm a physics.SE high-rep user". Of course, getting a wikipedia adminship is no easy business. RfA's are pretty gruelling.