This weekend REI was having a sale on VFFs, so I decided to take another sip of the Paleo kool-aid and bought a pair.
Well they seemed fine until today when I decided it had been long enough that I could try wearing them an entire day. After walking about 5 blocks on the sidewalk my tendonitis was acting up, and my ankles were feeling every bone-jarring step. Then I got to a section of campus where I had to cut across a grassy area and...100% better! So for the rest of the way to work I stepped on to grass or dirt sections wherever fesible and it was such a difference, even stepping on acorns didn't hurt compared to how pavement felt.
So I was thinking that maybe this is the reason most shoes have metal in them. The extra support we need from them is actually protection from the too hard artificial ground?