Does the SPI library use the internal USART?
I had a look at the source code for the SPI library. As suspected, it does not use the internal ATMega328 USART. This is useful to know because it means that the USART remains potentially available for other uses in any sketch that is using SPI. I suppose that it also makes the SPI library more portable because perhaps not all arduinen microcontrollers have a built-in USART