I have attended a couple of sessions on deploying Exchange 2007 on VMware Virtual Infrastructure and the big difference between these sessions and last year's Exchange sessions is the assumption that it's legit to do it. Last year running Exchange in a VM seemed to still be in doubt, but this year the discussion has shifted to more details about how to do it.
One key factor is the support that Microsoft now provides through the SVVP program that VMware joined and then used to certify ESX 3.5 update 2. I think that the other factor is that people are more comfortable with it and many more have actually tried it.
It's been fun to follow the acceptance of Exchange as a VM and I think that many other apps are following the same path (SQL, Oracle, SAP, etc....)
Todd