I was living in DC and my tenants in Pittsburgh called me in a panic because the hot water heater broke. I called Mr. Waterheater that afternoon and the next day, they came out and installed a new one. I was able to make all of the arrangements (appointment time, payment, etc.) over the phone and my tenants reported that the technician was v. professional.
About 6 or 7 years later, I'm back in DC...and the water heater broke (yes, I'm back in Pittsburgh and for the sake of my water heater reliability, won't be moving there any time soon). Mr. Waterheater honored the warranty, the only downside was a $100 service fee, but it was cheaper than a new tank.
The only negative was that in both cases, the technician did not haul away the old tank. It would have been nice to have that done, but certainly a minor thing, since my tenants were able to take the tank to the curb where it got picked up the next time we have trash collection.