Office blogs discussing the the Office "12" User Interface
Jensen Harris has started blogging about the new Office "12" UI. Folks who attended the keynotes at PDC, got to see the first look at the new UI. From everyone I talked to, there is a lot of excitement and I heard over and over that folks can't wait to get their hands on Beta 1.
Jensen's blog should be a great read. He has a lot of knowledge around the evolution of the Office user interfaces and will probably mix in a lot of historical information on top of all the new stuff.
Also, Steven Sinofsky talks a bit about learning from the past in this blog post: http://blogs.msdn.com/techtalk/archive/2005/09/12/464152.aspx. It's a great read.