I've done it barefoot. Usually on a clean place like turn for packed sand. I'm far more prone to it now since it has been done in the Marines with gear one. When I get a chance in a week or two, I will be going to the doctor to get my ankles and knee evaluated. I have a feeling I have stretched tendons out to the point where they can't heal all the way.
I wear my Vibrams for sprints in grass or something similarly soft. Also for weight lifting. But not distance. I'm just as likely to break a toe (two of my friends have broken multiple toes with the minimalist shoes).