Mostly hobbyists, but there are a few exceptions. For example, the Makerbot Thingomatic 3D printer uses an Arduino Mega as its mainboard. Makerbot had more than

Mostly hobbyists, but there are a few exceptions. For example, the Makerbot Thingomatic 3D printer uses an Arduino Mega as its mainboard. Makerbot had more than $1M in revenue in 2010. I suspect that Makerbot sticks with the Arduino Mega because it makes their hardware hackable by their users, which is worth more to them than the reduction in parts cost (minus the non-recurring increase in engineering expense).