Last week I posted a description of how to write a peer-to-peer chat application using WCF, with a WPF GUI layer isolated from the application logic, all built using .NET 4.0 and Visual Studio 2010.
The basic approach was adapted from the article at http://msdn.microsoft.com/en-us/library/cc297274.aspx
where Amit Bahree and Chris Peiris did something similar, using winforms for the GUI.
I’ve now posted the complete source code as a .zip file here.
Just unzip, open the solution file in Visual Studio 2010, and hit F5.
Also, here’s a video to walk you through the whole development process.