Reading through the licensing documents of the upcoming System Center 2012 I came across the FAQ document that touches on the number of OSEs (Operating System Environments) that you are entitled to run for free based on which level of the Suite you purchase. See below for excerpt from FAQ document.
13. Can I extend a Server ML to manage applications running on the public cloud? Yes, with the License Mobility through Software Assurance benefit, you can assign Server ML to manage applications running on a public cloud infrastructure. System Center 2012 Standard licenses allow you to manage two virtual OSE in a public cloud, while System Center 2012 Datacenter licenses allow you to manage up to eight virtual OSEs in a public cloud. For more information, see the Microsoft License Mobility through Software Assurance Customer Guide.
Only 8 OSEs in System Center 2012 Datacenter came as a surprise to me as the Datacenter version of every product Microsoft sells has come with unlimited virtualization rights. This is one of the biggest advantages Microsoft has over VMware at the moment where if you buy the Datacenter version of Windows, you get Hyper-V and all Windows Server OSEs are free of charge that run on this host license. This is the same with the current and future System Center Datacenter Suite for your private cloud, but if you extend into the public cloud, after you get to your 9th VM in the cloud, you will have to start layering additional System Center 2012 licenses, muddying the easy licensing tracking professed in the current marketing of the new suites. Just think about having hundreds of OSEs in the public cloud. For most, 8 VMs in the public cloud may be high or just about right for many organizations today, but with the push toward the public cloud this number will soon surpassed.
Not long ago I thought it would be unthinkable to have hundreds or thousands of VMs or consolidation ratios of 50 VMs to a host, but with the maturing of hypervisors and modern hardware leaps, these numbers are very attainable, as too will be managing more than 8 OSEs in the public cloud.