The official release of Silverlight 3 is already a fact and at Silverlight.net you can find the latest files for download. For more information on how to get started with the new Silverlight 3, pay a visit to our Get Started page.
With the official release there are a lot of changes that will affect in some way the Silverlight 2 and Silverlight 3 Beta applications. As the list of changes is pretty long, I will overview only the most interesting of them, but to be fully intact with the new release and to convert your application as fast and easy as possible, be sure to read this breaking changes document, provided by the Silverlight SDK team.