I have received a reply back from Microsoft technical support who have assured me that the issue is being worked on, but, in the mean time, the instances are fine to use, the lack of activation will not have any affect on the services running on the server.
To avoid any false hope, I'm going to start by saying that I have yet to fix the issue I am about to describe. There are a couple of suggested fixes linked within this post, but, none have so far worked for me.
I've ran into an issue recently where Windows Activation fails when creating a new Windows Azure Virtual Machine using either of the images of Windows Server 2008 or 2012 provided within the Image Gallery.
The VM gets provisioned and launched successfully and I can connect to the machine via Remote Desktop as expected. However, when connected, I get the "Windows is not activated" message and prompted to activate now.
When I attempt Activation, the result is Error code 0xC004F074, as illustrated below:
The suggested fix in the Knowledge Base article, linked above, did not work for me, I continue receiving the same error.
There is also an MSDN forum thread, Windows Server 2012 Datacenter Not Activating - Windows Azure. This contains some more detailed steps suggesting another method of solving the issue, but, these did not fix the problem for me. Your mileage may vary.
The Windows Azure team are aware of this issue and know that it is affecting a small number of Azure customers.
Azure support are investigating, despite the Virtual Machine feature still being in a preview stage, so hopefully they will be able to find a working solution. If they do, then I will update this post with details to hopefully help out anyone else struggling with this issue.