I mentioned earlier that Prism was renamed to Composite Application Guidance for WPF:
and yesterday the Composite Application Guidance for WPF has been released as RC1 with very few changes expected before it will be released in a couple of weeks:

At this point I think Microsoft Patterns & Practices are mainly working on the documentation. If the documentation is anything like the Smart Client Software Factory and Web Client Software Factory, it should be a real treat to read. The one thing about Patterns & Practices compared to other open source initiatives is that their documentation is first rate. You typically get:
- When and when not to use the Composite Application Guidance WPF
- Key Scenarios
- Problems Solved by the Composite Application Library
- Design Patterns
- References to other Composite WPF Guidance Best Practices
- Quickstart Tutorials
In fact, the Composite Application Guidance for WPF comes with several quickstart samples that start you out slowly and after your brief introduction you get the StockTrader Reference Implementation ( StockTraderRI ) that is a sweet Composite WPF Application that shows off the Composite Application Library, Unity IoC for dependency injection, and a bit of Enterprise Library Logging Application Block and Exception Handling Application Block for good measure.
We will be presenting the Composite Application Guidance for WPF at the next Day of Patterns & Practices in Tampa, Florida. In the meantime, I recommend downloading Prism and running through the samples. I will be creating some tutorials in the near future.