I have a couple of pairs of these great flip-flops with an arch in them.  I ordered my typical size 10 and they are just a little bit too small and have to go back.  The ribbon strap is great and the "mushy" sole feels wonderful.  Once you try these you will never go back to your cheesy flips.
There are no half sizes so I guess these shoes are running smaller than they used to.  Order up a half size if possible.