Wen you install the version of Windows 8 Enterprise from MSDN (and I presume TechNet), it assumes you will have a KMS (Key Management Server) in your domain.
When you try to activate it will fail (unless you actually do have a KMS…) – I saw errors about KMS and missing DNS names.
Lastly, there appears to be no way to enter or change the product key to the one provided by MSDN.

The solution: you have to change the product key using the command line:
Open an elevated command prompt, and type the command “slmgr.vbs /ipk ” followed by your MSDN / TechNet product key.

slmgr.vbs /ipk AAAAA-BBBBB-CCCCC-DDDDD-EEEEE

After a few seconds you should see a popup window letting you know the product key was successfully installed.

Note: this is based on the instructions here: http://social.microsoft.com/Forums/zh/genuinewindows7/thread/ce677eb0-7d97-46d6-81df-a05dca1c2b85

In my case, this immediately removed the “Activate Windows” overlay as well as the desktop watermark with the version and build number.