While talking with the salesperson at the kickboxing gym I recently visited, one thing that he mentioned that made sense was that many people stretch at the wrong time. I have always been under the impression that stretching before any workout is good for you. In general it is, but the key question is: When is the best time to stretch? Stretching while your muscles are cold could lead to tearing and muscle strain. Cold muscles do not have sufficient blood supply and are not as flexible.
From what I have been hearing and reading, a better time to stretch is after a warm-up consisting of light exercises. A nice warm-up increases blood flow to your muscles making them more pliable. It is important to keep the stretching light to moderate as over-stretching can lead to injury as well.