Sorry for the hiatus - lots going on in Xbox-land, what with GDC going on and all our projects are moving ahead full steam regardless of that, too. I was watching G4's Attack of the Show online and someone mentioned that the Xbox team had moved on to other projects. I can assure you the people sitting in the offices around me are still working on keeping Xbox 360 fresh for our customers - new features for Xbox.com, Xbox Live, the console, peripherals and development tools are all under way.
In my previous post, I talked a lot about the current development environment we have for Xbox 360, internally as well as externally. Many people responded to that in the comments crying out for the ability to write games in C# for Xbox 360. By now, it is probably pretty obvious why I didn't answer the questions even though I specifically said I would :)
I'll see if I can get one of the developers on the XNA tools team to give you all more detailed info about both XNA Framework and XNA Build - how they work, what features they have, etc.
And since I know you all have been waiting for it, I am preparing an article for later this week that will cover a lot of info about backwards compatibility. Watch for it after GDC dies down a bit.