Because operating system UIs have barely evolved since the 80’s, it’s interesting to follow the evolution of Microsoft’s Longhorn and especially its graphical user interface: Aero.
“Avalon is the code name for the Longhorn graphics and media interface (GUI) that software developers will use to build applications. It will have two ‘tiers,’ called Aero and Aero Glass. Given its 3D nature, running Avalon will require some pretty hefty hardware.” –Longhorn Tastes the Apple, Richard Fisco
Microsoft has published some sample topics from the Aero User Interface guidelines including information on the new Windows file system which includes stacks, filter menus, breadcrumbs, direct editing, and notifications: “Although physical folders still exist in Longhorn, users rarely need them to accomplish their tasks. Instead, users interact with their data primarily through a number of specialized UI controls.”
Some additional screen shots from the "WinHEC 2004 build" of Longhorn feature the new "Jade" UI and some of it’s interface elements, which emulates the low-end Aero UI we'll see in the final Longhorn version.