A very common pattern for business focused applications is the "Composite Application Pattern". Over the last few months our P&P team has been working with industry leaders and the product teams in Microsoft to develop an sample application and a framework for building composite applications in WPF.
If you are looking at building a WPF business focused application, you should really check this out.. all the documentation, source code and even unit tests are included!
Check it out! Composite Application Guidance for WPF