I originally bought this as a quick on and off slipper to take my dog outside to do her business.  I've found though that it's almost an all weather shoe!  Just a few days ago I was walking in the dark and forgot about some collected water in the yard and stepped right into it!  No worries, it's waterproof enough so nothing leaked in.  I wear 8 E or extra wide so I ordered a 10 and it fits perfectly fine.  I'm not going to go run races with it or anything, just walk around outside for short spurts.

Edit 6/25/2013: It seems it repels water enough for instantaneous contact.  However I've found if you walk around on wet grass the moisture will seep into the slippers so eventually your feet will get wet.  The downside is when I take my dog out in the morning the slippers will get wet but they won't be completely dry by the evening.  Oh well.