I've owned the thong FitFlop Sandals for several years and they are THE most comfortable shoes ever.  More comfortable than name brand tennis shoes!  I finally opted for the Clog for cooler weather and am SO glad I did.  I was able to immediately wear them all day - no breaking in period.  The thick, cushioned sole is like heaven for my feet.  As others have commented, I had to order a size up from my thong size.