I have said I'd review these for some time now. Almost a year ago I purchased the Vibram Five Finger KSO's. I have over 100 miles on these. I bought the Five Fingers to hopefully make my feet stronger. I had run a couple of races over 50 miles and the thing that hurt the most was my feet. In the later miles of my 100 mile run, my feet were really hurting. There was no damage to them, they just hurt from being on them so long.
I must say the verdict is still out on whether they are helping. I have two road ultra's in the next month, and I may know more after that.
I have done most of my running on pavement or grass. I don't feel comfortable running trails in these. I have some friends that do, and Barefoot Ted has run hundred mile races in them. But I feel that I'd be courting injury running trails with these. I've stubbed my toe hard running trails, and if I hadn't been wearing trail shoes with their extra toe protection, I would probably have broken one by now.
Lately I've been combining heart rate training and running in the FF's. My heart rate training entails keeping my HR under 130. I usually do 5 to 6 miles in this range at a nearby paved loop. The most I've ever run in the FF's is 12 miles. Whenever I run hard, my calves hurt for several days. It's not a injury hurt, just a sore hurt that tells me I'm using muscles I don't usually use.
I guess I would say that these are fun shoes, but whether they are worth the money depends on what you want from them. But as most people advise, if you do get them, don't rush into long mileage with them. I would suggest no more than 5-8 miles a week for several months.