Lion to allow two virtualized instances of Mac OS X per machine
The virtualization story for Mac OS X is about to change dramatically, and for the better, as Lion's licensing changes the rules for virtual machines.
For some enterprise deployments, virtual Mac OS X environments are the Holy Grail: giving access to Mac-only applications on demand without having to supply Mac hardware on a one-to-one basis. While the vanilla version of Mac OS X has been theoretically virtualizable since the Intel transition (and in fact can be run on a virtual machine now under the right circumstances), the licensing agreement for Mac users up until Mac OS X 10.5 Leopard didn't allow virtual Macs, full stop.
Starting with Leopard, Apple began to permit limited virtualization of Mac OS X, with two major caveats: you could only run VMs on Mac hardware (no blade server racks full of HP gear serving out Mac desktops), and you needed a Mac OS X Server license, with a steep price. Under these conditions, virtual Macs were a luxury few took advantage of.