A number of self help authors teach some kind of variation of visualization techniques to help with focus and/or goal achievement. David Allen's "Getting Things Done" dedicates part of the book to using visualization to achieve goals. Tony Robbins also dedicates part of "Awaken the Giant Within" to visualization.
I have read about claims and experiments with athletes where one group spent more time doing physical practice while another group used visualization and had better results. However, I can never seem to find the referenced study. Does anyone know of well tested evidence regarding the effectiveness of visualization?
Update - Some additional background on visualization in self help books:
My hesitation with self help books is that they end up referring to an older self help book which will do likewise. A good example is Getting Things Done. The visualization section refers to a book from 1960 by Dr. Maxwell Maltz called: Psycho-cybernetics. The book consists mostly of the author's experience as a plastic surgeon teaching his patients how to use visualization to improve their self image. The book mentions a number of cases however does not provide a bibliography of references to any of these works. That and the fact the preface begins with: "The Secret of Using This Book to Change Your Life." made me a little weary.