The User Interface for Windows 7 will be familiar for many while at the same time different. The Aero interface is the one that will be used which many will remember from Windows Vista. But it will be changed. As of Milestone 3 there have only been a few tweaks. Such as the way the taskbar works. Some applications that are built in have the "ribbon" look and feel to it. But as of now there isn't much else that can be said for we have not handled the newest available interface.
When we get a build with the newest style interface we will make it know what the major changes to the interface will be.