If you're on a look for a powerful, extensible application framework for building service-oriented, rich WPF applications, here's a preview of what you can expect from Microsoft in (possibly near) future: Microsoft Code Name "Acropolis" CTP1.
[Taken from the help file] Microsoft Code Name "Acropolis" is a toolkit for creating modular, business-focused Windows client applications. "Acropolis" builds on the.NET Framework, and includes a run-time framework, design-time tools, and out-of-the-box functionality. "Acropolis" enables you to build reusable, connectable components and assemble them into working applications that are easy to change.
If you're familiar with Composite UI Application Block or Smart Client Software Factory, you'll feel right at home. Provided samples include Notepad, Outlook-styled application, a Portal (pluggable parts - interesting!) and RSS Reader. You'll need Visual Studio 2008 ("Orcas") to run those, and if you're ready to start from scratch, there are a couple of templates to start from:
... and the Acropolis Application Wizard will take it from there:
Certainly worth checking out...
[Update: read and watch more about "Acropolis" on its home page, hosted on windowsclient.net, a new community site, which replaced old www.windowsforms.net]