I was wearing them without the socks for a few hours and started to feel a little irritation so put the lightweight injinji socks I bought with the 5 Fingers which helped. I will ease into no sock wear so hopefully there will be no problems. The socks are great and when it's hot here may be preferrable in terms of odoras the sock will absorb the sweat, not the shoe. I'm thinking of getting a pair of KSO's. I thought fit was going to be an issue due to the size difference between my feet but I think it will work out.
CJ, I have not run in them yet but will try this week.