A while ago, when I was developing a lot of courseware, I got hooked on virtualisation. Virtual Machines are a great way to create a repeatable course environment, and if your course is Linux-based you can distribute the course images freely. I started off using VMWare; their Windows workstation was inexpensive, and their player was free.
I stuck with VMWare for years, and used it for more and more applications. In the good old days, when Dell were after market share rather than margin, I picked up a couple of servers for about £250 each - dual-core machines with 4Gb of ram and decent hard drives. I ran Ubuntu on them, and used VMWare Server to host several virtual machines.
All worked fine until VMWare announced that Server had reached end-of-life, and their remote desktop stopped working with current browsers. I found myself with a set of unusable VMs which represented many weeks of development and configuration.
At the time I was working on a contract a few desks away from Stuart Ervine, and he suggested I try VirtualBox. It's proved to be a more-than-adequate replacement for VMWare, who won't be getting business from me or the clients I advise in future. Of course VMWare were within their rights to end-of-life a free product, but they caused me enough grief to destroy six years of brand loyalty at a stroke.