From Jensen Harris
"My name is Jensen Harris and I work on the Microsoft Office "user experience" team. Our team is responsible for the overall interaction and visual design of the programs that ship in Office. Although we work very closely with the individual application teams (Word, Excel, PowerPoint, Outlook, etc.) to help solve difficult usability issues specific to those programs, our key responsibility is to design and develop the UI framework that people use to interact with all of Office. Some of the innovations that came from this team before my time working on it included red-squiggle spell checking in Office 95, command bars in Office 97, and Task Panes in Office XP.
In short, the team’s mission is to help make sure that you can find and use the functionality in Office as seamlessly as possible.
A wonderful blog I discovered via Kunal Kundaje blog that focuses on the next version of Microsoft Office, code named Office 12. Lots interesting information and screenshots of the new ui.