I was just talking with my mate Andrew about this today.  For those of you who have no clue WTF I'm talking about it, when opening a VM from file in VMware Workstation and ESX/i, it prompts you with a strange little question.  Did you move the VM or copy it?  And what does it matter?

Rather than explain it here, here's an excellent article on the topic.  I stumbled across this while looking for information on SQL configurationfile.ini settings.