All new, shiny, custom code, built on the Microsoft platform. I'm sure a detailed blog post will follow.

Very well done Mr. Spolsky. I've heard Jeff say in podcasts that he doesn't like threaded comments but without something like that to connect posts busy rooms become unreadable.

What about a hybrid where you can click on a question to respond and your response is still added at the bottom but when anyone hovers over the response a line shows up connecting the response to the question?

It already does that.

Insert oops reply here.

Any stats on usage? How many concurrent users / messages per second?

Any of it going to be open sourced? :-)