WHAT IS ARDUINO?
“Arduino is an open-source electronics platform based on easy-to-use hardware and software” as described from the Arduino Website.
Up until now, I still have no idea what it is all about even though I wastched it grom in the early 2000’s. I think its original intention is to get students to learn about programming as affordable as possible. You can download a lot of programs (called sketches) and their libraries online to study and modify them as well. In a very short time, you will be able to use the Arduino as a data logger, a device for playing pre-recorded sounds, graphical interface and more. However, I am still not familiar with them and so, the following are from my outdated opinions.
THE WHOLE BOARD
You will need to use the whole board in your projects. This could be a problem if your model kit (and its base) does not have the necessary space for it. You CAN make the whole Arduino run off in a single Atmel chip but you will need to invest in more resources and not just a USB cable. Anyway, here is how bootloading is done from the Arduino Website.
IT IS NOT FREE
This is something new to me but from the following article by Ms. Elecia White, it was an eye opener especially if your intention is commercial. It is great for learning, prototyping and all, but not so as a final product.