I recently helped Ashish publish a whitepaper on SEO of Silverlight Applications. The paper talks about some of the best practices for search engine optimization of Silverlight content. You can use these practices to make your Silverlight content discoverable on a Search Engine Results Page and to provide an acceptable experience for users who do not have Silverlight enabled on their browsers.

You can also download the whitepaper in a word doc, pdf or xps format.