>Invariably the first question they'll ask is which house the candidate was in

Are people actually asking this at the beginning of interviews? I'm a Harvard College grad, and that's a question I sometimes ask or am asked in social settings, but not in interview settings. When I've worked with interns or recent grads from the college it usually comes up eventually, but usually only after the internship/job has started and folks are starting to get each other.

There might be a selection bias here: the interviews were it came up were for juniors and the interviewer was fairly green as well. I think in one case they even had one year of overlap.