O Silverlight 4 Release Candidate já está disponível para download!
“What’s New in Silverlight 4?
Silverlight 4 delivers a full suite of powerful capabilities to business application developers, bringing the best-of-breed .NET platform to browser-based experiences. Silverlight provides an ideal platform for developing and deploying modern business applications for both customer facing and staff-facing applications. “
Encontre essas informações e downloads no Link http://silverlight.net/getstarted/silverlight-4/