> It takes maybe 5 minutes to wash up dishes

5 minutes of most sinks running is 10 gallons of water. (Most kitchen sinks are 2 gallons per minute).

> Dishwashers let you accumulate dirty dishes for a day or two which is the real advantage in water savings.

I agree. If you aren't filling the dishwasher then you are probably wasting water. However, a full dishwasher is going to be a real water/energy saver. Especially if you aren't washing the dishes before putting them in the dishwasher. (I know a decent number of people do that. It's a hard habit to break).

Who runs the water constantly? I don't. I put a stopper in the drain, get some hot water in the sink, then turn the water off. Wash everything, give it all a quick rinse, then dry.