I went running in my new Invisible Shoes today. I'm like the princess and the pea. Even though I got their thickest model (the 6mm Contact version), they felt plenty thin to me. I could feel the bigger stones or craters in the asphalt, and sometimes they hurt! But most of the time I wasn't being hurt and I enjoyed running in them immensely. I even forgot I was wearing them after a while and just enjoyed being outside getting some exercise. I especially liked it that with the cheap nylon rope laces and lack of leather or glue I didn't feel the slightest hesitation to get my feet wet in the surf on the beach.
There's no way in heck I could ever do a long hike or backpack trip in them though. They are way too thin. I can barely set up the kickstand on my scooter wearing them. The plus side is if you ever want to have the secret pleasure of being barefoot without actually being barefoot, these are the sandals to wear.