One thing I have not heard mentioned when people talk about virtual machines on Macs, is their ability to enable a single technician to have one or more different operating systems (and even more versions) running concurrently for providing support to users. Thus one support tech could be running a product in OS X, Windows XP, Windows 2000, various Linux flavors, at the same time and thus be able to walk clients through problems on any of this systems yet only have one piece of hardware. Much more space and cost efficient than having multiple machines.