The Microsoft Exchange team recently enhanced its position on virtualization. Most notably, the Unified Messaging Server Role is now supported with Exchange Server 2010 SP1 and later. In addition, combining Exchange 2010 DAGs with hypervisor-based clustering, high availability, or migration solutions that will move or automatically failover mailbox servers that are members of a DAG between clustered root servers, is now supported. The announcement was made in a post on the Exchange Team Blog, which can be found here.
The Best Practices for Virtualizing Exchange Server 2010 with Windows Server 2008 R2 Hyper-V whitepaper, which is designed to provide technical guidance on Exchange server roles, capacity planning, sizing and performance, as well as high availability best practices, was also released.