I've run with Vibram originals on asphalt and also run sock-footed on a treadmill almost daily.  At some point everything clicked, and I felt like all of my lower body joints were built to run this way.  There was a fluidity, and an optimization of movement that seemed to kick in.  Upper body movement is reduced, posture is improved, and overall strain is reduced.<p>And yes, the first few times my calves felt like they were going to explode.  Very sore and stiff.  I would wake up and nearly fall to the ground when I tried to walk.  After a few weeks this problem went away.