Michael Palermo, who works with the development team at Interface Technical Training, has done a video where he demonstrates how to create a Silverlight app that displays Twitter messages from various Twitter users. The video shows you how to make calls to the open source Twitter API via AJAX Page Methods, and display the results with faded text effects. You can watch the video and download the code.
Meanwhile, Steve Clayton writes a Popfly/Twitter mashup in about a minute and posts it on his blog. In the comments, Rohan Thomas writes that he found a way to post the widget on his MSDN blog. You can see it here in the left-hand column.