Yes, I mostly run on soft surfaces especially with running exclusively in flats. I run on dirt/rock packed trail, grass, asphalt and the treadmill. I avoid concrete or sidewalk running as much as possible.
I gradually worked my way into flats, with another pair of heavier shoe in the rotation, for several months (initially calves would be sore..) and eventually worked up to just wearing all flats for everything. I currently put in about 65-70 miles a week in them. Rotate about 3-4 pairs of the same kind.
What I like about wearing the flats, it definitely gives you more "feedback". In other words, I feel like I am more in tuned with my running since you can feel just about every step or discomfort.
Background, I am 5'4"-117-120lbs (yeah, I know I am little heavy for a runner or could be more efficient..) but thus far, I've not had a stress fracture and I wear custom orthotics (soft pliable) in them. Within the last 8 months, I've done couple marathons and several short races, all in flats.