This article by Richard Gray of the BBC raises some interesting points about stretching for runners. I agree with the last sentence of his "skip stretching if injury free" paragraph where he says it makes sense to stretch if you're recovering from an injury as it helps the muscle fibres elongate as they heal. This will give a physiological benefit. I would also add stretching though if you're not currently injured but have had a previous history of injury to the lower limbs.
Yes, for the uninjured stretching isn't likely to boost your running performance but it's also probably not going to do any harm either. Some people may use it as a mechanism to prepare themselves mentally for a run or as a wind-down after a run so there may be a psychological effect. I often see a small group of runners stretching together and having a chat while they're doing it so there may be a social benefit too.
For the very flexible runners out there (that he refers to as loosey-goosey) I would recommend foot and leg strengthening exercises rather than stretching.
I aim to put together a course on foot strengthening in the near future. Watch this space!