Yesterday I gave a talk at the Devnology Community Day about Unit testing Mvvm in Silverlight. Although only a handful of people came to my session, we had some nice discussions about writing tests using various frameworks.
One last note. Tuesday, November 9th Sixin is organizing a user group meeting about Design and Development Experiences in Silverlight at Macaw in Schiphol-Rijk in the Netherlands. There are some places available.