I think one of the most common ideas found in posts like Greg's is a gross misunderstanding of Stack Overflow's business model[1] which leads one to speculate that the only way to make a site like SO profitable would be to charge for access to answers. I've been a huge fan of SO for a few years and am happy to see you guys figured out a way to make the site profitable without resorting to a paywall.
It's profitable now, yes, and probably always will be. But what happens when the site inevitably stagnates but the investors keep demanding revenue growth?
More sites on different topics. Conferences. Books. Training courses. There are a lot of ways to monetize an enthusiastic audience that wants to learn.
I know I'm just an armchair quarterback, but there's a revolution in moving university courses online. Surely some of that will stick to the stackoverflow/serverfault/superuser crowd...
[1]http://meta.stackoverflow.com/questions/79435/what-is-stack-...