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but isn't there a flaw in the explanation that running usually happened on dirt, grass, and not on the paved streets of New York?This seems intuitive when considering the difference in impulse between a sidewalk and a grassy lawn, but I'm not sure it actually makes any difference if you have good form - the idea there being that your calves take all the impact (remember impulse, again), versus your knees. Muscles can develop - whereas joints and bones can deteriorate. There's a good illustration of this in the following link from Harvard, which elaborates on the mechanics of foot strike with pretty charts showing the force generated in different scenarios: http://www.barefootrunning.fas.harvard.edu/4BiomechanicsofFo...
I started running in VFFs in September, 2009, but didn't seriously commit to running in them until January of this year. I've since logged 1,200 miles in them and haven't looked back. I've done numerous 20+ mile runs in my Vibrams, including a marathon within the past month. There were 2,700 entrants at that race, but only two runners (including myself) wore VFFs. I haven't had any stress fractures or other injuries since I've started wearing them, even when logging around 60 miles per week. (This is not to say that I disagree with the other comments in this thread.)
I'm pretty passionate about barefoot running. I love to see others joining the movement, so I try to encourage best practices to those making the transition. If any of you have questions about how to take the plunge, feel free to follow up here or contact me via email.