Tony Soper alerted that there is some new content in the TechNet library for Hyper-V that is worth checking out:

Live Migration Step by Step Guide: http://technet.microsoft.com/en-us/library/dd446679.aspx - This guide details the steps required to perform a live migration of Hyper-V™ virtual machines from one node in a Windows Server® 2008 R2 failover cluster to another node.

What’s New for Hyper-V in R2: http://technet.microsoft.com/en-us/library/dd446676.aspx

Hyper-V Virtual Machine Snapshots: Frequently Asked Questions: http://technet.microsoft.com/en-us/library/dd560637.aspx