I like the old wisdom of; walk like a string is attached to the top of your head, pulling you up.
That makes sense to me, considering it's basically resisting the slouch due to gravity.
As for bare feet - yes! Feet have extraordinary grip, I love rock climbing bare footed, and I feel that my sense of balance is heightened because I can really feel the surface beneath my feet. Working out bare footed is awesome as well, it just feels pretty primal.
It's funny to realise, that in modern society, roads and pathways are all built relatively flat. Many a time when a newcomer comes on a bush-walk, they fall over quite a bit because they're not conditioned to walk on uneven surfaces. However, after a few bush walks, their balance becomes better. That's just one example of the instincts/skills we lose living in a modern society. I'm sure that wearing shoes all the time has ramifications as well.
I've seen plenty of documentaries where native tribes are all getting around in bare feet, they're tough as nails. But I guess we live in a society where we're pretty much guaranteed access to shoes for our entire lives, so the conditioning of the feet is not required. Which is ironic, because we (arguably) need shoes more in the bush, than you do on a city street walking on concrete.
As for sleeping on hard surfaces, I can only guess that bad posture sustained for the period of a night's sleep wouldn't be good for anyone, regardless of whether the surface slept on is hard or soft. So I guess the point is, it's not the surface that matters, as much as it is the posture that matters - and if a particular type of surface helps to maintain good posture, I guess it's the better way to go.
As for lurching whilst sitting, it's not only bad for the back, it's really bad for the shoulders. Rounded shoulders (pointing forward) as a result of sustained static holding in a slouched position is bad, and can lead to impingement, and believe me, that sucks. It's crucial for us in modern society to address this point, because (in general) we are frequently sitting at desks/computer stations and driving cars, both of which encourage a person to lurch forward for extended periods of time - which is totally unnatural.
