USATF is conducting a study to determine the effect of pre-run stretching on running injuries. The purpose of the study is to determine specifically if pre-run stretching of the three major leg muscle groups is beneficial for overall injury prevention or reduction. The study is not examining in-run or post-run stretching.
I'd be interested in being part of the study except for the fact that there is a good chance of being in the no-stretch group. I do very minimal pre-run stretching compared to most other runners I know, but I wouldn't be willing to go with no stretching at all before I run.