OS X Lion Allows Running Multiple Copies on Same Machine with Virtualization
Posted on July 1, 2011 by eli courey
The Gold Master version of OS X Lion was released to developers today and includes the final end-user licensing agreement, which reveals that users can run up to two additional instances of OS X Lion on the same machine. To do this, you would need virtualization software like VMWare Fusion and Parallels. This functionality was previously only available in the server version of OS X.
From the 10.7 EULA:
(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.
Source: Mac Rumors