None of the many suggested registry keys worked for me. I was able to observe that when the hated "Get even more out of Windows" screen was displayed, there was a UserOOBEBroker.exe process running. Killing that process doesn't make the screen go away, but doing a reboot does of course. I created a scheduled task to run every five minutes and reboot the machine if UserOOBEBroker.exe is running. The task runs a cmd file that contains a line like this:
tasklist /fi "imagename eq UserOOBEBroker.exe" | findstr exe > nul && shutdown /r /f /t 0
My complete cmd file writes a line to a log file, so I'm able to see that a reboot has been triggered. I've had the scheduled task running on 40 remotely-manged machines for a few days, and it's successfully freed up several machines that had the nag screen displayed.
I wish that MS could give me back all the hours that I spent struggling with this problem.