Last week I visited Science Friday in Second Life, and it was an excellent experience!!!
I immediately thought this might be an interesting format for Astronomy Cast.
Have you ever thought about doing a show in Second Life?

It was packed and the debate was very lively.
I think what they do is just stream a pre-recorded show into the site and then discuss the topic among the live audience
(this format should be quite easy to copy for Astronomy Cast)

Might be a good way to organize weekly or monthly virtual meet-ups, too.

Here's an illustrative video
And here's an article with more details