Just wondering what values you set your D to. Most of the time, a non-zero D leads to jittery responses since it draws from the change of values over short period of time. I usually only use P and I and only use D if the single is relatively clean and I need a faster response.
Arduino IDE is using C/C++ language so you can say that you learned C/C++ by using Arduino. I think Processing calls its program code sketch, which makes a lot of sense. It is used to visualize things so it is like a drawing or a sketch. Arduino/Wiring probably borrowed the term and claim to have used it for marketing purpose to make it sound less hard than code or program.