There used to be one or two places in the Seattle area that did this, but from what I hear the health dept shut them down because you can't sanitize fish.
I had one of these in Kuala Lumpur last year. Turns out they aren't such a great idea if you are ticklish. One of the little bastards got right into the space beside my big toe. I thought I was going to pass out.
While my mom and sisters and I were in Israel a couple years ago, some of our Israeli cousins took us to a natural spring that had similar fish in it. It was quite nice: rocks and greenery, a good mix of sun and shade, and water of a moderately cool temperature. The fish would come by and nibble if you stood still for more than five seconds, which took some getting used to, but it was rather invigorating all the same. But when I got out of the water to head over to the bathroom, I saw a man holding a makeshift bandage over a bleeding cut on his toe. I asked if he'd stepped on a rock or something, upon which he informed me that he'd been bitten by what must have been the biggest fish in the lake.
And then later we left in a hurry because someone shot someone else. I was off in a crevice at the time, and thought it was just firecrackers until my mom came over and got me.
This apparently operates on the same principle as "maggot therapy" for necrotic tissue. The fish (or maggots) will eat only the dead skin and leave the live untouched, thereby getting rid of everything you want to get rid of while leaving behind everything you want to keep.
But when it was done my feet were smoooooth.
And then later we left in a hurry because someone shot someone else. I was off in a crevice at the time, and thought it was just firecrackers until my mom came over and got me.