In 2002 a study was published that suggested that stretching before taking exercise was unnecessary. Australian physical therapists reviewed 3 studies that evaluated the possible benefits of stretching out before and after exercise on soreness. Now one of the original authors has enlarged their study, and reported their results in the Cochrane Library.

This time the authors identified 10 studies of stretching before and after athletic activity; 9 were done in lab settings and one in Australian-rules football players. Although all the studies 'were of questionable quality', pooled results showed a high degree of consistency. Pre-exercise stretching reduced soreness one day after exercise by, on average, 0.5 points on a 100-point scale. Post-exercise stretching reduced soreness one day after exercise by an average of 1 point on the 100-point scale. In other words, no effect worth talking about. There were similar findings up to 3 days after exercise.

This more or less proves the point - stretching before or after exercise doesn't reduce soreness. You'd think that this would be fairly well known after the first study, 5 years ago, published in the British Medical Journal. But the physical therapists at my gym make a point of telling clients to 'stretch well out before exercise as well as afterwards' to avoid sore muscles. Some news travels slowly.