Long Zheng has put up some photos from the "Design principles for Windows 7" session at PDC. These really are general principles that we should all take into account designing software experiences.
The example of the jump lists in Windows 7 is interesting. By right-clicking on an application icon in the task bar or start menu, users will see a list of recent files opened in that application. This provides a great shortcut, and helps people to think in terms of the work they need to do (the document or file), rather than the application they need to use.
Of course, placing items in a right-click menu introduces a challenge of discoverability. An alternative was to place an 'arrow' icon to indicate there is a pop-up menu available. This would solve the discoverability problem, but introduces new problems:
I'm sure other alternatives were considered as well.
Did I mention that interaction design is all about compromise?
You can also see a video of a demo of the Windows 7 UI from PDC here: Windows 7 Demo