We finally shipped Prism 4.1 for Silverlight 5. You can find the documentation at www.microsoft.com/prism. The documentation is the same between Prism 4.0 and Prism 4.1. The readme identifies the differences between the versions.
In the readme, I said that issue 5042 was fixed and it should be 4052. Sorry about the mistake.
In the next 1 – 2 months we will start planning an update to Prism for .NET 4.5. Let me know what requirements you think we should address.