I've seen Atmel chips in commercial devices before. Off the cuff, I don't remember what, it was a while ago and I don't go ripping apart functioning appliances to see what ICs they use very often. So take that for what you will.
Reliability of any MCU itself will be dwarfed by the system in which it's in. It's just not the part most likely to fail. The I/O pins aren't meant to interface with the outside world, so you need to make sure there are hardened interfaces wherever you expose connectivity. (MAX232 for serial, for instance ..) And the PSU of course is a big deal. With good filtering, sensible protection circuitry, and proper software design, I'm sure an AVR will run for as long as your product has any useful purpose.