With the release of OS X Lion, Apple updated their licensing agreement to allow the virtualization of Mac OS X under programs such as VMWare Fusion and Parallels. This functionality allows you to deploy different sandboxed installations of OS X on a single machine.
VMware may have closed the performance gap between Fusion and Parallels Desktop with its latest Fusion 3.1 update. The free update is available now to all Fusion 3.x users, and promises big improvements, especially in 2D and 3D graphics. According to VMware's director of personal desktop products, Pat Lee, this update is all about speed, speed, and more speed.