The Blend 2 Service Pack 1 contains a secret ingredient that can be activated by installing the WPF Toolkit and then setting a Registry value. In a nutshell, this ingredient is Visual State Manager support for Windows Presentation Foundation projects....(
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Read the complete post at http://blogs.msdn.com/expression/archive/2008/10/30/blend-2-sp1-wpf-toolkit-visual-state-manager-for-wpf.aspx