This is not intended to start a fire storm, but I wanted to let the boards know that I have been training for the Boston Marathon in racing flats (Nike Streak xc, and marathoner) and have had nothing but a good experience.
In the beginning runs took more effort than expected because I was using so many small muscles, but after having built up my mileage gradually I feel that my stride is more powerful and my legs feel more stable than in the past. I have been very injury prone in the past and as of yet (knock on wood) have avoided any injuries.
I discussed this experiece with my chiropractor and he said that he is not surprised. He said that the chiropractic profession in general has seen many more injuries such as high ankle sprains than in the past because (in his opinion) people are running in shoes that prevent them from building the necessary stabalizer muscles as they build mileage.
As I said, this isn't meant to upset anyone, but I would suggest every runner try integrating a day or two of running in flats into their weekly routine as a trial to see how it feels. I think you'd be surprised by the possible benefits of relying upon the strength of your body.
Just my thoughts, enjoy the miles.