Jeremy Likness has created something that is quite close to being the perfect sample application: It has about the third of the scale of a real-world application: not just the usual two forms, but also not the size of a book. There’s a lot of concepts used in the right way, but you don’t need to read the manual before you get through it. The whole thing looks like something that you would write as proof-of-concept for a real project. I think Jeremy has really met the perfect balance of size, complexity, and simplicity.
Oh, and it is about using MEF in Silverlight that really make sense.