"I am trying to understand how this would work for user testing."
I'm not really sure what you mean by "how this work," but let me say this.... There are a couple of ways to accomplish what you are trying to do. First, you get the VM in the state that you want. Just before taking your user through the process, simply click on the VM-menu, then "Take Snapshot." The length of time it takes will depend on a lot of things -- your disk speed will be the most important. When you have finished with the user, use the Snapshot Manager to restore the previous snapshot. That's it!
Another way to accomplish the task, and this is what I generally do because it's faster for me. I get the VM to the state that I want and then shut it down. I then copy the VM directory to a new location and use that VM. In your case, when it's time to work with another users, you simply make another copy of the first VM.
Good luck... 
Dumb question Peter.
How did you get text from my original message into your message...with the shaded background?
Thanks