I'm using it. My horse had a mishap with her tail and lost the black part of her black and white tail. I've been putting it in for a few months, and I really don't see the difference, but I see my horse all the time, so I could very possible just be missing it.
BUT, I do also use it on my filly, who has this incredible knack for taking out chunks of fur all over her body. So far, I've used it on several bald spots, and all of them have grown back within two weeks, sometimes even sooner. =]