I am up to 34% of my mileage barefoot (that is out of 20-60 miles per week, depending on the season). I still prefer grass when I am shoeless, though I have been crossing roads more and more. I am a fairly serious competitive masters runner in NJ. 45 years old; running for 31 years. I fell into barefoot running a year ago when I realized that most of my injuries were from falling off the elevated heels of my running shoes. I chronically twisted my ankles. I went on a rampage and purged most of the running shoes from under my bed - anything with over-built heels and too many motion control devices.
In addition to twisting ankles, I have also suffered from plantar faciaitis and achillies tendonitis. Not since running barefoot, though!
I began mixing barefoot running into my training routines a little bit at a time. 5 minutes per day, every other day, adding 5 more every week. Now I run up to an hour barefoot, both distance and intervals.
Running barefoot has changed my footstrike from heavy heel striking to one where my entire outside edge strikes at once and my heel is only down for a nanosecond. I have been able to race faster with less intervals and speedwork. I can't run on any grass surface anymore without thinking, "I should be barefoot." I constantly seek out parks and other large grassy areas where I typically do repetitive long laps as part of my longer workouts that start and end with shoes. I am kind of addicted. It just feels good and right.
Many other runners in my running club have seen me running barefoot now and we talk about it. I tell them how it has changed my running style and has banished injuries. I tell them I don't fear glass, that some of the stuff that falls off trees can hurt so I stay out from under them, but 99/100 steps are pure pleasure. Some are using barefoot running as part of their cool-down after hard runs and track workouts.
Now, when I buy training shoes, I look for shoes with little or no difference in sole height at the toe and heels. I run in racing flats and retro-shoes a lot - that is how I got through the NJ winter while retaining barefoot running feet. I also have the advantage of a summer job running a pool so I can be barefoot all day.
So though I am not a 100% barefoot runner, I am convinced that it is an extremely important part of a well designed training program.