In MSDN about Silverlight 3, there is new feature called Application Library Caching.This tutorial is to explor this new feature and verify that it does work.

Question is why is this compelling new feature?

In Silverlight 2 there were couple of ways to take advantage of browser caching and it was to download resources. In Silverlight 3 there is support to accomplish this out of the box. When application gets compiled and re-deployed we do not want the resources to be re downloaded unless the resources such as images changed because it takes too much time. Just imagine having WMV as resources and you are forced to download everytime new Silverlight application is deployed!