ilbob,
Indeed our tankless is less efficient. How many minutes a day do you actually draw water? For these, relatively few, minutes it's running at not much more than 50% efficiency. A tank-type heater, while more efficient, is experiencing a steady heat loss 24 hours a day. Even well-insulated, this loss adds up.
Our winter gas bill didn't change much as the furnace draws so much more than the water heating that savings weren't very obvious but it became VERY significant in the summer.
They've been using these for a long time in Europe where energy costs are much higher than here.
More recently we replaced our furnace with a 95% model. that's when the savings REALLY started.