I just went on a zip line for the first time, and climbing their tallest ladder was pretty unnerving. I don't have a great fear to begin with, but my the wow-I'm-really-hear effect has definitely gone down. Maybe if I had done that exact zip line in VR, it would have helped? I do believe VR can help with phobias and PTSD (http://www.virtuallybetter.com/), but I wonder if its benefit goes down with exposure (complete speculation!).