I just reviewed this sample and it is really shows off Expression and Silverlight 5. It is entirely possible that you could base an entire business off of this project by John Papa! It shows how to implement the 3D features in Silverlight 5. It provides a project that allows you to create a house along with a bill of material (think parts list). If you have family that is in construction, this might be for you.
Check it out at: 3D Housebuilder demo
John Papa has a great blog at http://www.johnpapa.net
John Papa is not shown in the picture.