I believe in RIAs because developing an HTML/AJAX application is just painful. And I believe that Silverlight provides an excellent RIA solution. For two great examples of Silverlight in action look at:
These both look and feel like desktop applications but are running safely in your friendly browser.
Be aware that CodePlex has a project for windows4all.com (http://windows4all.codeplex.com/) but all of the source code is not provided. Just a Visual Studio shell application. It would be great to sneak a peek at the code under the covers.