I wrote an article about this last year that was in Marathon and Beyond. I referred to a Cabadian doctor who's studied this for years and years. Essentially, he says that the foot needs feedback to function properly while you run. Cushioned, corrective, "supportive" shoes block the feedback and you end up slamming your foot into the ground harder in an attempt to get the feedback.
I switched to racers full time in 1995 and have not had one injury since. I made the switch because my knee had been killing me and not getting better and had goten worse as I spent money on more "protective" shoes. Since the article was published I've gotten several phone calls or e-mails from people who read and cleared up problems by switching to racers or to very simple shoes. Personally, I think that one of the reasons the Japanese can do all the mileage they do is because they train in racers.
I made the switch all at once, no transition or anything. I assume this won't work for everyone, but it's worked for several people. I haven't found the durability issue too problematic. I've got an old pair of Nike Pegasus racers that I've had forever and that show no sign of impending death, and I was close to 1,000 miles with a pair of Asics Gel-Paws. I just took out the insoles at about 300 miles and replaced it with a Spenco.