I first wore VFFs for a 7-mile hike. For the first twenty minutes, I was constantly aware of sensations in my feet. Thereafter, I got used to my shoes.
After each of the first three to four hikes (each hike was 8 to 10 miles long), I used to feel fatigue in the muscles in the bottom of the foot for about a day. I suppose these muscles had atrophied in regular shoes.
For the first ten hikes, it was my firm belief in the philosophy behind VFF's ("go natural - let your feet develop") that helped me persist with them - it was not comfort. Over time, I got used to them to the extent that I don't enjoy hiking in regular shoes any more. Now, I find VFFs really comfortable. My experience reminds me of a quote I read on FaceBook recently:
"Most people never run far enough on their first wind to find out they've got a second. Give your dreams all you've got and you'll be amazed at the energy that comes out of you." - William James
My first pair was the original VFF, the Classic model (which are not advertized for hiking / trekking). During hikes, I slipped a couple of times in these shoes when I was walking faster than usual (almost jogging) going downhill: once on a grassy patch and once on a fire road with loose tiny pebbles. Also, I didn't feel confident hopping on stones in water during creek crossings - I had to be extra careful. So I bought a second pair, the KSO Trek -- these have much better traction. I never had any problems on any terrain with KSO Trek. The KSO Trek were more 'bouncy' because they have extra material in the sole - Initially, I didnt like this bounce but within a hike or two, I got used to it.
Over the last two years, I've done day hikes in Vibrams on all sorts of terrain: sand (long beach walks), rocks (Mt Whitney / Death Valley), river crossings (Henry Cowell), redwoods and so on.
A common question I get asked is: "what about stones?" Stony terrain is indeed the hardest for my feet but I have never been injured in VFFs. An interesting thing I noticed along Mt Whitney trail which is full of rocks, big and small: my mind and body had been trained to automatically choose good cushioned landing spots for my feet! This was not conscious effort - it came naturally.
After about 800 miles with KSO Trek, the sole was still in great condition but the upper part of the shoe had fallen apart. So I started wearing my original Classic model. By this time, I had started using hiking poles for long, strenuous hikes. I noticed that with hiking poles, the lack of traction in the Classic model didn't bother me. For example, during a Big Sur hike, we had to traverse some steep sections on exposed fire roads - with hiking poles, I could negotiate these sections comfortably.
In 2012, I started jogging in VFFs. I'd never jogged before, so this was new to me. Despite a couple of years of hiking in VFFs, my natural jogging stride didn't seem to be the 'midfoot landing stride' - it required conscious effort. I noticed that I really enjoyed uneven terrain found on trails - I also become faster on trails than on paved road!
Since January 2012, I have been wearing VFFs to office as well. Ever since Sergei Brin started wearing VFFs to office, other employees followed suit.
I have also gone barefoot on a couple of hikes, for about two miles each. Maybe, some day, I'll start doing barefoot hikes without VFFs.
My experience with Vibram Five Fingers (VFFs) has been highly positive. Over time, my feet got stronger. I really enjoy hiking in VFFs.