This is a great white paper for anyone evaluating what storage solution to deploy for Exchange 2007...  There has been a lot of discussions about storage and Exchange 2007 and how the debate has changed from when we were architecting Exchange 2003 deployments.  I am in the middle of a blog so will add to the debate shortly I hope.  In the meantime this white paper is definitely worth reading..

Storage Design for Exchange Server 2007 - How Microsoft IT Exceeds High-Availability Targets with Large Mailboxes at Low Costs Based on New Storage Designs