VSM4WPF
While next release of WPF (3.5 SP1) won't yet align with Silverlight's "Parts & States Model" by not introducing VisualStateManager into its API, it's good to know that VSM is definitely coming to WPF. Even more, John Gossman has just released a prototype of his VisualStateManager for desktop WPF, which is compatible with Silverlight Beta 2 VSM implementation.
Before VSM is built into the core of WPF, this prototype lets us explore and play with this "new way" of controls' state transitioning in WPF applications. Sweet.