Chipkit compatibility with Arduino
It will work well with most basic sketches and examples you will find on the internet that do not do too many AVR specific things. The arduino environment is effective at hiding the details of the actual processor from you, but it does not mandate that separation. You are still welcome to import the chip-specific header files and directly change specific registers, access pins directly, and interact with the chip on a much lower level. Any code that uses the avr specific headers will not port cleanly to a pic system without modifications.