I live and die with my virtual servers on my local computers to test proof-of-concepts; PowerShell scripts, backup/recovery scenarios, and many other important aspects to my job as a Web and SharePoint Administrator.
But one aggrevating thing is the Windows 2008 Activation feature that creeps up if you do not manage it.
I found a great TechNet article on how to extended the grace period in Virtual Environments. This will work with VMWare Workstation, VirtualBox, Virtual Server, and Hyper-V. In theory, it should work in other virtual enviornments.