There's a presentation on Windows 7, direct from Microsoft using the new Silverlight plugin. It highlights some of the benefits and improvements, and might be worth a read if you are interested in the main changes:
http://www.microsoft.com/learning/_silverlight/learningsnacks/win7/snack01/Default.html
http://www.microsoft.com/learning/_silverlight/learningsnacks/win7/snack01/Default.html