Okay I have to preface this by saying I really am USUALLY not into this kind of hocus pocus.
I worked for a therapist that was trained and certified in Reiki. I didn't think much of it and I mentioned my neck was tight. She approached me from behind and I had no expectations - she didn't mention Reiki.
She held out her hand and barely touched my shoulder and there as this flow of something like energy-like the way it would feel if you had your hand on a hose and could feel the water running through it. It was really surprising. So I have learned not to discount stuff I don't understand.
I believe it could be effective if done correctly.