I bought one new in 2004 for a condo. The heater sits in an enclosed utility closet with 3 other water heaters. The space is really confined and prone to be dusty. Shortly after installation (a couple of weeks). There was no hot water! The installers would not help because they said it was the manufacturers problem. The company did deal with the problem. Now, almost 6 years later, I can't remember what they said the problem was, but I think some part was replaced - rather than putting in an entirely new unit. Now for more than a year the pilot keeps going out. And of course the explanations have been that it's because the heater is in a confined spaced with little air flow and full of dust. No - I say it's poor design. It is COMMON for hot water heaters to sit in a place like mine does. In fact, for more than 30 years hot water heaters have been in this space and these problems didn't occur until I got the AO Smith. Don't buy it!!
Editors Note: The flame for the pilot uses a minimal amount of air compared to the main burners. Hopefully the closet where these water heaters are located comply with mechanical code concerning combustion air.

After 3 years I had to have my igniter replaced - I could have had it "cleaned" but it looked brand new and it was under warranty. I don't think that this is "normal" wear and tear on what is supposed to be a heavy duty hot water heater. It's gas - the 75 gallon version that feeds a house with a family of 6 people. There is no way this is over-used or set up in a "dirty" environment. It's in a partially finished basement. So I can only attribute this to poor quality and give it low marks for reliability. I'm sure my review is tempered by the cold shower I took this morning.