Ok, Arduino is a good technology but is it used professionally? Is the quality good enough to be used for professional purposes?
In theory, an Arduino board could be used in some low-end professional products (i.e. where the performance and memory limitations aren't an issue). The build quality of the official boards is certainly good enough. The only issue they would potentially have is making suitably robust connections -- i.e. anything plugged into a female header would have the potential to get shaken loose.
In practice though, using an Arduino board would only make sense for extremely small-scale projects, where only a few units will be produced, and where there will be a minimum of external circuitry.
A commercial project would normally have a custom circuit board designed. That allows them to economise on space and features, eliminating unnecessary costs. Even if it only saves a small amount per board, it can make a big difference if you're doing mass-production.
With that said, a professional product could certainly use an AVR microcontroller or similar at its heart (much like the Arduino boards). Atmel was producing chips long before Arduino was around, and their products are well known and widely used. The choice really depends on the needs of the individual project.
Yes, you can also use an Arduino for professional usage. The Arduino is actually just a prototyping device and easy to use for people at home/school. I suppose there might be products on the market which were developed using an Arduino. But the most important thing is the Atmel MCU inside the Arduino which can be used for anything. But, if you wanna know if the ATmega328P-PU which is used in the Arduino Uno is a common MCU used by professionals? The answer would be no. Everything has to be smaller and better so it'll be more likely to find the same MCU like the Arduino Leonardo, Mega etc etc.
Examples where professionals might use an Arduino for as base (The end product will only contain the MCU of the Arduino):
- Kid toys like an Simon Says Game, Line following toy cars etc etc.
- Small industrial products like an automated tape dispenser.
- AVR programmers.
- Card readers.
Yes, I work for an engineering design house and we use Arduino frequently to prototype ideas for clients. It significantly speeds up the time to get a proof-of-concept device in the hands of the client and their potential investors.
We have found though that there is significant work to get from an Arduino-based prototype to a commercially-ready product. Essentially you have to start again and design a completely custom printed circuit board, which is a relatively expensive exercise.
We are now developing a platform that is compatible with the Arduino IDE, but uses surface-mount modules rather than the Arduino shield system, allowing it to be manufactured in an automated surface-mount facility. Check it out if you are interested at duinopro.cc. We are in development stages at the moment, but already have hardware and are mainly working on our website, and designing new modules.