There's a new study out that, I think, pretty much demonstrates that. I've looked at the study and have described it, along with other thoughts, in this blog entry: http://ahcuah.wordpress.com/2013/03/02/vibram-transitioning-bone-injury/
Why is everyone always looking for companies to issue warnings about everything that anyone could possibly do stupidly with their products? If people want to buy something and use it, it should be each person's own responsibility (and freedom) to decide what they do with it and how much they think about the consequences.There probably should be warning with normal shoes, but the companies are too big and powerful and have everyone in their pockets, including researchers. Interesting how no one has gone to a barefoot culture and given them shoes and measured the rate of injury.