OS X Lion will enable Mac users to run multiple copies of OS X on the same machine. This functionality has previously only been available on Mac OS X Server but now OS X virtualization is coming to, well, to OS X.
News of this came a few days ago when Apple released its Golden Master candidate of Lion to developers containing an updated EULA which sates:
(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.
This news should be particularly useful for enterprise users and developers who can now test their software under different environments for compatibility purposes.