Not much insight here I know, but I was researching this topic for a friend today and thought the collection of links might at least be useful!
Microsoft Virtualization: Best Choice for Exchange Server
Should You Virtualize Exchange 2007 SP1?
Exchange 2010 System Requirements
Microsoft Support Policies and Recommendations for Exchange Servers in Hardware Virtualization Environments
TechNet Webcast – Microsoft Virtualisation Best Practices for Exchange Server (Level 300)