I have been able to do this for years. It is not a compulsion for me. I do not count letters every time I hear words. But I can do it on command. My friends and family are amazed when they say a word and I can instantly tell them how many letters are in it. I have found that prime number words (11, 13, 17) sometimes give me a split-second hesitation. I do compulsively read the numbers on license plates, but that is the only compulsion I have. Maybe I just have a little OCD in me. It is great to hear from some other people who know of this. Get a copy of City Slickers 2: The Legend of Curly's Gold. There is a scene where the guys are sitting around a campfire and Jon Lovitz's character does this same thing. Until now that is the only other place I've ever heard of anyone being able to do this.