wow, there sure are a lots of stuttering threads around. Anyway, my therapist used to tell me that stuttering is just a bad habit that we develop as kids, another known reason for it is that it could be hereditary, 90% of stammerers have someone in their family with the same problem, other than that causes are largely unknown. Stuttering is basically caused when the speed with which your vocal chords produce sound is unequal to the speed of your thoughts, slowing down is the best way out.
And if you are serious about eliminating it, go join a therapist. He can properly tell you how to do the exercises and can monitor your progress in a systematic way, when you do them at homw, it just doesn't work. Best of luck!