As you may have already noticed: the RC1 of Silverlight 1.0 has been put online on the weekend. Since the last beta there have been fixed around 2000 (!) bugs and added some more features. English downloads are available here:
Because of the big changes RC1 is not 100% compatible to the previous beta versions. That means that a lot of demos currently available will not work after you have changed your version to RC1. Joe Stegman  wrote on his blog about the breaking changes between Mix and Version 1.0.  In the current silverlight.js you will see some comments on the changes, too.
As you may know when reading my blog I'm waiting for the first Silverlight 1.1 release. So, what happend for this alpha version? Well, the .NET part didn't change, but the Core Runtime of the plugin is the same as 1.0 RC1. You will find the new bits here: