During the plenary of the 2008 ESRI International Conference, Ismael Chivite demonstrated a Silverlight map viewer for ArcGIS Server. The source code to the Silverlight map viewer is available here on ESRI Resource Center's code gallery.

The Silverlight map viewer is a proof of concept developed by the ESRI Prototype Lab.  The viewer is based on the MultiScaleImage control which is also known as DeepZoom.  DeepZoom is essentially a technology for viewing an image pyramids.  A popular implementation of the DeepZoom technology is the Hard Rock Cafe Memorabilia web page.

The map viewer is based on Silverlight 2 beta 2 which is cross-browser on both Mac and Windows machines.

The Silverlight map viewer can be used for any ArcGIS Server cached map service.  However there is one "gotcha".  Due to a limitation with the MultiScaleImage control, tile scales must double sequentially.  For example, if the first tile scale is 1:1000, then the next scale must be 1:2000 then 1:4000 and so on.  The viewer uses the ArcGIS Server REST API to query the map service tile structure.

Two sample web applications are published on ESRI's website for you to try now.  The first application displays the World 2D Imagery layer from ArcGIS Online.  Click here or the image below to display the web application.

The second sample web application demonstration the JavaScript API exposed through the Silverlight map viewer.  Currently there are only a few API's exposed.  View the source code of the following application to understand how to manipulate the Silverlight (e.g. zoom and pan) using JavaScript.