If, like me, you'd seen references to XPathNavigator, maybe in IBlogThis discussions, but hadn't used the class yet, then the latest MSDN TV slot Passing XML Data Inside the CLR, presented by Don Box, is worth watching.
XPathNavigator is based on the XPath data model which is also new to me. It seems to be a cut-down version of full XML data model, details in the W3C working draft.
The resources for the talk point to some sample custom XPathNavigator/XmlReader implementations at DevelopMentor.
I like the MSDN TV format. I find the MSDN show format a bit long-winded whereas the MSDN TV slots are concise and to the point, covering just enough material to keep you interested during a coffee break. If I had time to sit through a full MSDN show episode I think I'd rather watch a movie on dvd instead.