Not the c++, the functions they give for simple things, so you don't have to read the manual to find out for instance the name of the GPIO port register (a very small step) or learn the boolean operations to diddle only one bit (another very small step). This is fine for an educational toy but arduino libs (and even the boards, ha) are showing up as part of finished products in the market, that's really sad.

Is my personal opinion that c++ doesn't belong on an 8 bit anyway.