On my second day of running in the FiveFingers, I was able to run a couple of stretches without having to think about the position of each of the bones and the tension in every muscle below my waist. It just clicked a couple of times! I ended up with a very fast, very short stride, with my heel hitting just hard enough to make me worry about it, but not enough to rattle my teeth. To do that, though, I needed to concentrate on everything above my waist: my posture and the tilt of my body: very straight posture with a slight forward tilt. At the same time, it all had to be very loose and relaxed. As with avoiding hard hitting on my heels, that posture is exactly what's required for sprinting. So, this is turning out to be pretty much what I noticed the first time out - a slow-motion sprint. Instead of using full power going forward, I'm doing it all at about half power, and all of my leg motions are about 3/4 speed.
Another thing I noticed with the FiveFingers: because they have almost no sole, you can feel hot pavement pretty well. That's not fun.