I've seen this in a few places, but it's rare because of all the energy (heat loss and energy required to drive the circulation) that gets used up when the water is recirculating but nobody is using it--which is most of the time.

I was recently in Iceland, and since a lot of heat is geothermal, recirc would probably make sense, but I can't remember having it. Maybe it's the pumping cost? Although natural convection driven by the difference in density between hot and cold water might make up for at least part of that.