I bought a 1/2 size bigger but should of gone up one entire size.  For shorter runs they are great.  Excellent for running up hills. Nice feel.  I ran a 25k using a pair of montrail running shoes and after the race my feet were swollen and my size 10.5 minimus would hardly fit.  Very tight.  For longer distences i would recommend one size larger than your running shoe.  50k plus feet get hammered.  Ran a couple of trail 10k with the smaller size and no problem.  I did order another pair same model 1 size larger for long runs.  On the 25k i talked with a runner clydsdale who was wearing a pair and loves the shoes.  In my experience i like these better than the vibram 5 fingers for running.  One the road i used mizuno wave riders for 10 years but on the trail i am transitioning from montrails to the new balance minimus.  Note: the lower back of caves had to adjust to the shoes but now the road running shoes have a different feel.  It will take time to adjust but they do have the barefoot feel.  With the front design i doubt that i will lose toenails.  Toes seem to spread out on downhill vs. the front toes jamming.  The shoes are light.  Happy running.