Guardian has an interview with Jeff Raikes of Microsoft:
If you poll Office users, there’s a couple of things that really stand out. One is that they really see that Office is very important to what they do in their jobs, so they care a lot about it. The second thing is that they’d like to be able to do even more. They recognise there’s a lot of capability in the product that they’re not getting to today. So the research that we put into designing the user experience was to address that issue: to help folks get to more capability and get things done faster and easier. Our research shows they can use 65% fewer keystrokes and less mouse-travel.
People want a results-oriented interface: they want to get things done. So that’s the most notable step with Office 2007.