I have been using VirtualBox for the last few (several) years and I love it. While my main working laptop is chockful of software, it is never enough so I use lots of virtual machines, all being created, run and managed through the excellent VirtualBox. It means that I can install some very beta software on a variety of platforms, test them out and then get rid of them. I also have virtual machines to ensure that I have a very clean environment for training. For example, I have a windows 7 virtual machine loaded with Python 2.7 that I use to train and practise Python almost exclusively. Pity that I can't really use VMs for gaming....
I tinker with Linux (lots of distros), different versions of Windows and I even have a VM running 'Haiku' (go on, get it here) and I am seriously thinking of getting an emulator and running the old Spectrum, BBC Micro and a few others. I miss the old games!