I've recently had the opportunity to join a client's team building an ESB solution using the Windows Communication Foundation (WCF) with requirements for security, logging, load distribution across a managed group of hosts, and more. As you can see from my list of books here on my site, I spent some free time over the holidays reading up on WCF. It seems that everything published about WCF so far just covers how to write and host services.
The best organized book I found that presents all the key concepts and somewhat covers extensibility through behaviors is Pro WCF by Chris Peiris and Dennis Mulder. I've also reviewed Programming WCF Services by Juval Lowy, which has a somewhat shotgun approach development with WCF, great for coding, but doesn't really cover WCF extensibility.
The best references I've found on extending WCF are Mark Gabarra's blog and this great, detailed MSDN article on WCF extensions by Aaron Skonnard, which gives full examples of extending WCF in a variety of ways, including behaviors. I'm currently prototyping a WCF service with extensions at a variety of points and will post more as I make progress.