John Papa did a demo of this impressive 3D house build Silverlight application at the MIX11 Keynote.

Microsoft have released the source code for this as a free download. The quality of the rendering is certainly impressive and it seems they are making 3D support a cornerstone of the benefits of using Sliverlight 5 when it is released. Certainly something to keep an eye on if you are in the building industry. Anything that makes high quality 3D renders easier and cheaper to build, will definitely be welcomed.