I've given a few talks at the various Embedded Systems Conferences on the subject of the Arduino as a real prototyping tool. I've designed and built a number of custom Arduino-compatible boards myself. I've become an advocate for the Arduino as a legitimate tool for the commercial engineering world. But sometimes advocating isn't enough. You need to see it in action to believe it.
Here at Screaming Circuits, we build a lot of different types of boards for a lot of different companies and organizations. The are boards being used for R&D, consumer products, education, medical devices, military things, space craft, Kickstarter companies, aviation... You name it, we've probably built it; up into space, down underwater, and anything in between. What's the engineering joke? "Civil Engineers build targets, mechanical engineers build weapons to destroy them." We build the electronics for both.
But, I've gotten off target. The point I wanted to make is that, if we're building it, it's most likely a professional/commercial caliber product. The other day, amongst the many other designs being assembled out on our shop floor, I spotted a shield, full size for the Arduino Mega. I don't see anything close to every job that we build, but it's gotten pretty common for me to see something Arduino compatible - either in form-factor, code compatible, or both, out on our shop floor.
One such example is the electronic badge we built for the upcoming Embedded Systems Conference in Boston. Our partner, Sunstone Circuits provided the PC boards, Synapse-Wireless designed it and provided the wireless modules. We bought the rest of the parts and built it.
With as many as I'm seeing these days, I can only conclude that the Arduino has entered the commercial design world.
Open source the pod bay doors, HAL