I just found out this afternoon that hot water recirculators exist. In a nutshell, once you've turned off a hot water tap, these things will take the water back so that it can be reheated. Then, when you next turn on the hot water, you get hot water, instead of cold water for a minute.
It's an interesting idea... sort of seems like the ultimate in laziness. Waaahhh, I don't want to wait for my hot water. I want it now! But, it does save you a little money on water. In about a decade it would pay for itself for a family, and during that time you've had the convenience of always-ready hot water.