We've released RC0 of Silverlight 2. This is intended as a developer only release - neither the Silverlight 1 nor Silverlight 2 Beta 2 plug-in will auto-update to this release. This is an opportunity to test your Silverlight 2 applications against RC0 to ensure they will be ready for final release. There is also a preview of SP1 for Expression Blend which targets Silverlight 2 RC0.

There is a full list of breaking changes between B2 and RC0, I've pulled out the contents list below as a summary:

• Important! Migrating Older Code to the Newer Release
• ContentPresenter now derives from FrameworkElement instead of Control
• Layout Rendering Slightly Changed
• Cross domain hosts of Silverlight must set the right MIME type for XAP (application/x-silverlight-app)
• Exceptions now thrown in HttpWebRequest.EndGetResponse()
• Font URI is Restricted to Assembly Resource
• Browser.HtmlElementCollection replaced with by Browser.ScriptObjectCollection
• Exceptions When Changing Some Properties on an Active Animation
• System.Windows.Controls.Extended.dll renamed to System.Windows.Controls.dll
• VisualStateManager Changes
• KeyDown Sent Synchronously
• MeasureOverride/ArrangeOverride on Canvas Now Sealed
• UriTypeConverter moved to System.dll
• HtmlPage.UnregisterScriptableObject Removed
• RenderingEventArgs Changes
• ContentPresenter and ContentControl Changes
• Removal of FileDialogFileInfo Type and OpenFileDialog.SelectedFile(s) Properties
• Removal of FullAccess Option on the ExternalCallersFromCrossDomain attribute in the Silverlight 2 application manifest
• KeyFrameCollection Changes
• Request stream must be closed before calling HttpWebRequest.BeginGetResponse()
• HtmlWindow references on Safari/Mac will no longer evaluate to true
• Address property removed from all WebClient EventArg classes
• Constructors Made Internal
• Exception type change for System.Xml exception type
• Cannot create classes in XAML that do not have accessible constructors
• Get AG_E_UNKNOWN_ERROR in Silverlight 2 but not in Silverlight 1
• Platform looks for generic.xaml as a resource at themes/generic.xaml
• HTTP Polling Duplex OM Changes and Reengineering
• Breaking change to Silverlight native hosting IXcpControl COM interface
• Content-Type is allowed on cross domain request by default
• Enforcing delegate type check when two delegate objects are combined
• Miscellaneous API Changes

All the relevant links and downloads are available on Silverlight.Net.