I know alot of runners that use the new five fingers or minimalist shoes. They have all said that the change is significant when you run in them. They said because they were wearing running shoes with lots of cushioning and support for so long, that once they started running in the minimalist shoes, they had to in essance relearn to run. The muscles in their feet were not strong enough to do the running and had to run slowly to build them. Most people said after the first run, their feet hurt something awful, but eventually got better after a few weeks of running in them.
Chicago Shamrock Shuffle 8k 57:02 4/10/11
Chicago Run for the Zoo 10k 1:06:51 6/05/11
Chicago Half Marathon 2:33:49 9/11/11
Chicago Hot Chocolate 15k 1:34:20 11/05/11
Chicago Polar Dash 1/2 Marathon 2:21:11 (PR) 1/21/12
I run exclusively in Vibram 5 Fingers. I struggled with shin splints and knee issues in regular running shoes, decided to try the VFFs and haven't had a problem since. It is highly recommended that you transition into them slowly and give your body a chance to adjust. There is a barefoot runner's forum that was very helpful to me.