Hi John Stewart,
I want also to mention on very importatn thing. As Steve mentioed Silverlight is only 2 years old and until now the tools we not very usable and good for every day development. But with VS2010 on its way and its design time capabilities we will see how really powerful the Silverlight technology can be. I'm sure that very soon the Silverlight install rate will be much better once the technology is adopted.
the Telerik team