Let Composite Application Block bashing begin. No, just kidding. Actually it's too late for that one. There were several blog posts over the last couple of days, but the one that started it all was this post from Resharper-Jedi Oren Eini. There were several responses in favor and several against his point of view, most notably from Chris Holmes and Sam Gentile. If you're interested, you should do some Googling about it.
I think that the truth lies somewhere in between. Although I've never created a Windows application with CAB, I can certainly believe it's hard to grasp initially. Besides some blog posts and some "Hello World" examples, I couldn't find some concise explanatory documentation. As with every framework, there is a learning curve involved (heck, I'm still learning new things about NHibernate every day).
On the other hand, I strongly believe that the P&P team is doing a good job. They've created a framework for building Windows applications using patterns like IOC/DI, MVP, MVC etc. necessary to have a testable design. Could they've come up with a simpler solution? Sure they could. It doesn't matter to me (everyone knows that you should go along with the third release). What does matter is that they create awareness amongst developers that putting all your UI logic in the code-behind model is not the best thing since sliced bread. In order to create maintainable solutions, it's necessary to have a testable design that adheres to low coupling, high cohesion. I believe that Microsoft is doing a terrible job at the moment in encouraging developers to write maintainable software, except for the P&P team. They are the light at the end of the tunnel. Although their efforts are not perfect either, I hope that they can make a difference.