Sad to see it go. As an original hardware engineer who moved into the OS world Gadgeteer allowed me to re-awaken the love of gadgets with low startup investment in my busy schedule. The fact that I was writing an operating system and device driver model at work in C# was all the better....
But it never caught on like Arduino, and now RaspberryPi and others. Having implemented many Gadgeteer projects and re-implemented in Arduino/RaspberryPi, etc. I will say the Gadgeteer is the fasted to up and running. Even as an expert with scopes and logical analyzers I spend many more hours on hardware, code, and drivers for Arduino style projects than plug and play Gadgeteer, as long as you don't go outside the boundaries.
But since it did not take off, the cost of a "deployment" system was prohibitive. Which is why the Arduino style was in the picture, leading to double coding in C# for Gadgeteer for quick "Startup Weekend" stuff (actually won one), and C/C++ for production units.
As others have said, I have over $1k invested, but I learned a lot and did some great projects.