Mac OS X Lion Supports Running Additional OS X Instances Within a Virtual Machine
Mac OS X 10.7 Lion can run additional copies of itself in virtual machines on the same machine, this is the first time that Apple has allowed this feature outside of Mac OS X Server. This was discovered by MacRumors:
Running separate instances of Mac OS X should be possible under virtualization solutions such as VMware Fusion and Parallels. This functionality allows you to deploy different sandboxed installations of OS X, typically for enterprise purposes.
The Lion GM End User Licensing Agreement (EULA) states that users can run up to two additional instances of Mac OS X Lion without purchasing additional licenses. Here is the segment of the EULA addressing virtualization, courtesy again of MacRumors:
(iii) to install, use and run up to two (2) additional copies or instances of the Apple Software within virtual operating system environments on each Mac Computer you own or control that is already running the Apple Software.
It should be pointed out that the virtualization license is separate from the personal use license.
Developers, IT, and engineers will find virtualization particularly useful, since it allows for rapid deployment of customized instances, and the testing of various configurations and software without impacting the core operating system