In our house, the master bath is on the complete opposite side of the house from the water heater, and we have to run about two gallons of water before it gets hot, and if we wait more than 10 or 15 minutes between showers, the water in the pipes gets cold again, and we have to run another two gallons. In other words it isn't just the water in the shower pipe, it is the water in the full pipe between the heater and the shower.

I've just started looking into either getting a tank-less water heater in the master bathroom or a recirculating system to save water. I like that the recirculating system would help with the entire house, not just that one bathroom, but it is looking to be quite expensive and wasteful of energy, unless we can do something like have switches in the bathrooms and kitchen to manually turn on the recirculator for a few minutes before use instead of running the water for a few minutes.