twice:
Honestly, the 8 bit AVR controllers seem to be used mainly by hobbyists. I have looked for a list of professional devices that use AVRs but I found no convincing evidence they have serious applications in practice.
That's utterly ridiculous.
Other posters have pointed out that a semiconductor company does not build a successful business model based on selling to hobbyists.
Yes, the Atmel AVR processor is used in all different kinds of applications, commercial and industrial. I'm not at liberty to discuss specific customers, or numbers, but they are definitely used by professional embedded systems.
Remember that the Arduino boards and software are targeted mainly to non-engineers. That's a good thing, as it introduces embedded technology to large groups of people that don't normally have direct access to it. But if you need to put together a robust system, with the ability to write software for such a system, it is very much being done with other tools out there.