Sauces: How do you use cornstarch and arrowroot to make clear thickened sauces?

Michael e-mailed the Kitchen Shrink with this question. He said that he wanted to make clear dessert sauces and had heard that cornstarch or arrowroot was the answer but he had never used either. Cornstarch and arrowroot are similar ingredients to work with. Both have almost twice the thickening power…