I've decided that running in Luna sandals is more comfortable for me than walking in Luna sandals. I've never worn flip flops and it has taken me a long time to get used to the hemp lace of the Lunas between my toes. That said, I couldn't feel the laces at all when I was running in them. They are fabulous running footwear (when the weather's warm).
Because they have no upper, your toes can splay as far as they need to. There's plenty of breathability, too. There's just enough thickness in the sole to allow for comfortable running even on gravel.
I think they look so great with the suede footbed that I couldn't bring myself to wear them through the mud, even for the review for Living Barefoot (which is coming soon).
You really have to have strong feet to run in these for any length of time, however. The muscles in my feet were a little sore the next day. :)