My guess is not too long. I have no personal objection to prostitution, and I think it should be legalized. But the context of the act is vitally important here. Spitzer broke the trust of both the groups to whom he apologized this afternoon. He deceived his family; that's a matter for him to resolve with the four women most important in his life (his wife and three daughters). More central to the question of his resignation is the violation of the oath onto which he entered fourteen months ago. The Governor has a solemn obligation to faithfully execute the State's laws. This is not the first time since Spitzer assumed office that his fidelity to that obligation has been called into question. His administration's questionable use of the State Police to smear Senate Majority Leader Joseph Bruno, while not criminal, were highly suspect and directly at odds with Spitzer's promise to "change the ethics of Albany."
And now, we have this. It was a bulldog mentality that won him national acclaim - Spitzer referred to himself as "a fucking steamroller" last year. That stubbornness and zeal, while great for an attorney general, aren't always the best qualities in a chief executive. They'll probably cause him to resist the tide of public opinion, but eventually, he'll resign - as he absolutely must.
One last (slightly flippant) comment on this: Princeton for undergrad, and Harvard Law...come on, what did you expect?