Who is "someone", what are his or her credentials and what is it about stainless tanks that he or she believes unsuitable for domestic hot water?
Why would you be willing to believe anonymous sources from the web preferentially to "someone"?
Stainless steel is used for cooking pots, tea kettles, flatware, sinks and dishwashers. It is used in breweries, distillaries, and almost all food processing.
There are a variety of domestic water heaters (mostly instantanious) made from stainless, and many marine potable water systems use stainless.
So, what do you think?