When you implement the entire System Center Suite of Tools, you have a comprehensive management stack that has onsite into the physical hardware of your virtualized systems, the virtualization layer, as well as the applications running in the Guests. Not only that, but it can manage and monitor your physical servers as well. This means that with one license, I have the ability to manage and monitor what would take multiple different licenses from MANY different companies to do the same thing. By the way: System Center Virtual Machine Manager 2008 R2 (VMM) supports and manages not only Microsoft virtual machines, but also those from VMware ESX. Additionally, VMM supports new Windows Server 2008 R2 features such as Live Migration, hot addition/removal of storage and the latest networking technologies. For more information please see here.