Most workloads can run comfortably in a virtual environment these days as long as that environment is built out appropriately. At Westminster College, we recently virtualized almost all of our remaining physical workloads, including our Exchange 2007 services, SharePoint 2007 systems and SQL Server databases. In addition, we've been building out our Exchange 2010 and SharePoint 2010 environments in our vSphere infrastructure. These new workloads have never seen a physical server.
We are currently in the process of migrating from Exchange 2007 to Exchange 2010, moving mailboxes to the new system. At present we've got about 800 or so mailboxes moved. The beauty of the virtual environment is that we've been able to start a bit small and add resources as it became necessary so that we can build a system that meets our needs without wasting resources. We've hot added RAM and additional disk space on the system volume to the server as we undertook the process -- with no downtime. It's been a fantastic experience for us so far and it's strongly reinforced the decision that we made early on to do this entire project in VMware rather than on physical hardware.
Even the "older" workloads -- the ones that underwent a P2V process -- are working extremely well in their new homes. In short, our efforts have ben somewhat aggressive, but they are paying off handsomely.