Mike Taulty's series of Prism (Microsoft's MVVM framework) for Silveright videos is awesome. It took me several days to watch all the videos and do the sample code along with the videos, but it really drove home Prism. I think there are at least 8 hours of actual video. It was well worth the watch for me.
He starts with simple concepts in a console app, and then about a 1/3 of the way through the videos takes the concepts and starts applying them with Prism/Unity in a Silverlight app. He tackles several common problems.
Mike Tault's Blog Post linking to his Channel 9 videos.
Here is the Microsoft Patterns and Practices (the team that wrote Prism and Unity) web site for Prism and Unity.
That should get you started.