I haven't had a chance to run
I haven't had a chance to run in rain yet, and even if I had it only rains for like 10 minutes here anyways. From what I've heard though it shouldn't be to much of a problem, depending on how hard its raining and for how long. Basically its not a good idea to run when your feet are completely soaked, but that would happen more from sitting in a tub or pool, like Longboard said, than from rain. Now if you ran an ultra in rain and mud, your feet would probably start to soften up and you might have some trouble. I guess we can just toughen our feet a bit, focus on our form, and hope we don't have to run 50-100 miles in mud.