The fact that XAML is just XML empowers a lot of interesting scenarios. In my MSDN Article for an RSS Hero Bar, I used a XAML Template to drive the look and feel for the applicaiton, and then use the System.XML.XmlDocument to load and manipulate the template. You can see the full article here: http://msdn2.microsoft.com/en-us/library/bb410109.aspx
Joshua Allen has taken these concepts and has moved it to run on the Silverlight 1.1. client, cutting the amount of code needed to only 10 lines. He then went on and built a MiniCache class, which is sort-of like an XmlElement node class providing an in-memory cache with forward-only replacement and writer functionality...great stuff!!!
The full post is here: