Yes, it is available on Technet (see here).
I have upgraded my existing BizTalk 2006 installation on Windows Vista (yes, I’ve been using unsupported configuration, but it ran pretty well for my needs).
My first interest after the installation was to check whether the WCF adapters were in place. And as You might guess – they were. Also, documentation were updated to reflect the change. Docs now include the walkthroughs for various WCF adapter usage. As we are talking about WCF, there is one thing to add: WCF LOB adapter SDK. I would suggest to look at that as well, especially take a very close look at this blog.
Ahh, and RFID is also one cool feature that is available for R2 users (Available in all versions). Dear wholesalers, retailers, etc. – please be sure you have investigated the functionality and opportunities.
If You are planning to install R2 into your machine and avoid unnecessary issues, I would suggest to allow setup to download the prerequisites, because the documentation points to the wrong URL.