To that end, I keep a clean baseline image with only Windows installed. When the time has come to pave my dev environment, I clone this VM and start re-installing (thanks Chocolatey!).
However, rather inconveniently, I found that even though the baseline copy of Windows had been activated, the cloned VMs somehow knew that something had changed and needed re-activation.
Normally the trigger for this is a change of MAC address, but VBox allows you to keep that the same (the VMs are never running at the same time, so having the same MAC address is not a problem).
Eventually, this got annoying enough that I did what I should have done in the first place, to the internet!
Apparently, the secret is to set an extra property called the hardwareuuid:
VBoxManage modifyvm --hardwareuuid
Once this is set, any cloned VMs will inherit it. No more activation!
(Piracy is bad, m’kay. But I paid for Windows, and I want to use it as I wish).