One of the smart client technologies we've talked a lot about in the past is Windows Presentation Foundation. One of the key points made during MIX06 is that there is an increasing number of display types that devices uses. The application UI may need to scale from the 7 inch screen of the ultra portable mobile computer to the 17 to 21 inch screen of the typical desktop to the 50+ inch screen of a high definition TV (through Windows Media Center or a Windows Media Center extender).
Windows Presentation Foundation allows you to create a single UI that dynamically scales across the various display sizes. This is something that is very difficult to do with today's presentation technologies.
Also, Windows Media Center may not sound like it is relevant to federal developers. There are situations, however, where applications need to be displayed on large TV screens and accessed through a remote control. For example, in Network Operations Centers. Windows Media Center provides a great platform for building these types of applications. In Vista, it will support WPF.
-Marc and David