Ask HN: Thought Experiement: If HN ran ads, how much would PG earn

HN is a high traffic site. I expect that if they ran banner ads or contextual ads, like google does, they would make good cash. I am curious to know how much money they could make this way. If you were in charge of HN ads division, what kind of ads would you run and what CTR, CPM would you expect?

EDIT: Just from a traffic point of view. Lets also assume no one leaves the site because of that. Just trying to see how the traffic-revenue correlation works in this case.