tankless water heater/boiler?

Thanks to everyone who helped out with the direct vent/power vent water heater and boiler question a few days ago.
Now I have another question. I found many sites with tankless water heaters which have very high efficiency. But I am worrying whether this will cause unstable water temperature in practice. Could you point me to some reviews, or share your own experiences with me?
Also, I am not clear what is the difference between a hot water boiler and a water heater. I know that a boiler has a lot more heat capacity (in BTU/hr). Howeve, I don't know whether it has a water tank as well, and whether the size of the tank is important (it is not listed in many specifications). I also appreciate help on that issue.
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Habitat for Humanity in Mt. Pleasant SC has been building homes using tankless water heaters over the past two years. We check owners regularly and have had no complaints. TB
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On Sat, 06 Aug 2005 13:49:59 GMT, "Feng Ouyang"

A boiler is an indirect system using steam to heat the water. They were popular in recirculating systems, such as found in laundromats, but are gradually being replaced by tankless heaters.
Hot water 'boilers' generally weren't designed to heat the water in a single pass, and required an external tank and recirculating pump, making them rather inefficient.
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-john
wide-open at throttle dot info
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