Scoble and the Channel 9 team just posted an interview with Brian Jones, program manager on the Microsoft Word team. You have to check this out.
I can't wait to see the Reference Schemas to see how different they are from Office 2003. They mention they will have an update for older versions to make them work with the new format. He also mentioned new file extensions: docx, .pptx, .xlsx.
Brian has also just started blogging, so you need to check out his site. I just subscribed to his RSS feed.