I presented this application during the MIX11 Day 2 keynote to demonstrate the new 3D features in Silverlight 5 along with a few other new Silverlight 5 features including RelativeSource Ancestor, Data Binding Debugging, Implicit DataTemplates, and Binding in Style Setters.
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You can download the source for the 3D Housebuilder on the MSDN Code Sample Gallery
Read more: John Papa