Tim Heuer has done a great post on the Silverlight 4 released. Availability of tools announcement.
BEFORE you run off to Tim’s blog please READ THIS
If you need to continue doing Windows Phone 7 development, stick with the Visual Studio 2010 Release Candidate for now! The updated CTP of the Windows Phone developer tools is not quite done yet. Information about updated tools availability will be forthcoming on these tools. Stay tuned.
When you visit Tim’s blog you will be prompted to “upgrade your version of Silverlight to Silverlight 4”. Don’t do it if you are still working on the VS2010RC w/ Silverlight 3 dev tools (see above).
Yesterday after installing the Silverlight 4 client, I needed to “uninstall Silverlight” and reinstall the Silverlight 3 Developer runtime to continue development in VS2010RC w/ Silverlight 3.