I recently moved my Windows 8 test machine from Virtual Box on my desktop to my Hypervisor. But instead of installing Windows 7 first, i installed Windows 8 directly. I could do this without trouble, but once it was installed, I could not activate it. After a little bit of google I found following solution:

Open regedit and change following dword to the value 0 (after a clean install with the oem image it will likely have 1 as value):

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Setup\OOBE
DWORD: MediaBootInstall

After changing the value open a command line window as administrator and run following command and reboot the computer:
[batch]slmgr -rearm[/batch]

As luck would have it, a disk in my Hypervisor failed just a couple of hours after writing the draft of this article. Naturally it was the disk with my newly created and activated win8 machine on it and obviously I did not bother to back it up just yet. I did not publish the article immediately, because I wanted too look into Microsofts stance on activating an upgrade this way first. But after this crash, i have to come to the conclusion, if they do not allow it then screw them. I know that Microsoft has a lot of seriously odd licensing clauses, some of them might not even be legal in your country and thus automatically void. But they usually do not enforce the extremely odd stances at all or not for private users. Also it is possible, to have upgrade versions of Windows since 3.11 and everything would be OK on the license front. But i am fairly certain, that even Microsoft would not expect a user to start upgrading is computer from Windows 3.11.

As a fun tidbit, at a Microsoft licensing seminar i learned, that it is not actually licensed to connect with Remote Desktop onto a Windows XP Machine. The Background of this is, that since Windows 7 this is only allowed with a Windows 7 Enterprise license (there might have been some kind of package needed on top of that), and since the Windows XP license does not actually say anything about the use of Remote Desktop it is not licensed. I seriously doubt, the will ever try to enforce that, since it is ridiculous, and possibly not legal in my country. But it shows how far removed from reality they are.

I found this helpful bit of information in a topic over at Hardforum.