At long last, I finally got a pair of Vibram Five Fingers KSO Treks, the VFFs designed for trail running. The sole is a tad thicker, and there are some lugs on the sole to help grip on the trails. I tried them out on a short 5 miler at Tandy Hills Natural Area, which I wrote about a few months ago here. I had run there before in my VFF Sprints, and was uncomfortable for much of the time on the rocky trials. With the slightly thicker soles, the Treks made a big difference. I still stepped carefully on the rocky sections, but my feet didn't end up feeling pulverized. One side issue--any of you VFF wearers have an issue with grass and weeds getting stuck between your toes? Some of the trails there are not well-travelled, and are a bit overgrown. There were a few times I had to stop and pull big weeds out from between my toes.