Silverlight 2 Beta 2 now provides everybody with a commercial go-live license.
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.