Silverlight 2 Beta 2 now provides everybody with a commercial go-live license.
Scott Guthrie has the lowdown as does Tim Heuer on how to get started. Scott Barnes throws in his comments as well.
Once you upgrade your browser to Silverlight 2 Beta 2 you will no longer be able to run Silverlight Beta 1 applications. This means that if you have published a running sample on the web built with Beta 1 you will probably want to update it to Beta 2 soon.
We have published a document that details the changes between Beta 1 and Beta 2. Also check out Shawn Wildermuth's What Changed in Silverlight 2 Beta2 and Upgrading your Silverlight 2 Projects to Beta2 posts for more details.
Best description on media enhancements including hooks to enable adaptive streaming is at http://on10.net/blogs/benwagg/Silverlight-2-Beta-2-is-out/
I'm thinking I need to slowly go out an start converting my samples as well.