This is the good stuff. I've previously used Prism in conjunction with Unity to create composite WPF clients in this manner, but it's useful to see a run through of the whole process (disclaimer .. I watched the first 40 minutes or so .. will continue with it tonight). It's tackled at a refreshingly rapid pace whilst remaining clear and entirely comprehensible too. Bravo.
(Apologies .. I added this comment to the Part 1 comments section .. it was supposed to be here)