I've just been catching up on the latest information posted to the Microsoft downloads site and I came across these three documents:
Exchange 2010 Tested Solutions: 500 Mailboxes in a Single Site Running Hyper-V on Dell Servers
Exchange 2010 Tested Solutions: 16000 Mailboxes in a Single Site Deployed on IBM and Brocade Hardware
Exchange 2010 Tested Solutions: 9000 Mailboxes in 2 Sites with Hyper-V on Dell M610 Servers & Storage with F5 Load Balancing
According to the downloads site : "In the Exchange 2010 Tested Solutions white papers, Microsoft provides examples of well-designed, cost-effective Exchange 2010 solutions deployed on hardware offered by some of our server, storage, and network partners"
These documents come in PDF format and they're not small as they range from between ~60 to ~100 pages each. I have downloaded them and shall take a look - but maybe not over the upcoming holiday period!