Ning Zhang has a post which illustrates the integration of Silverlight Toolkit with Visual Studio and Blend 3 after running Silverlight 3 Toolkit March 2009 Installer.
This is part of the series on design time implementation changes in Silverlight Toolkit March 2009 Release. This post illustrates the integration of Silverlight Toolkit with Visual Studio and Blend 3 after running Silverlight 3 Toolkit March 2009 Installer, and explains how it is done, so you can register your own Silverlight controls with Visual Studio and Blend too.