Joss Whedon internet musical

I'll be keeping a close eye on this as it develops for sure. According to various reports, Whedon is creating an online musical called "Doctor Horrible's Sing A Long Blog." I'm not really clear what that means or what it will look like but I'm sold. Neil Patrick Harris stars as the evil Doctor Horrible (!) and Nathan Fillion as the strapping hero. Here is the official site which doesn't have much on it yet, and then here is the fan blog...for the blog....