The hardware page for the Mini says the following about the pins:
digital i/o features
? all 16 digital and analog pins: GPIO
? pins 1-3: RS232 TX, RX, DTR
? pins 9-10: I2C SDA, SCL
? pins 11-12: UART 1 TX, RX
? pins 14-16: SPI MOSI, MISO, SPCK
? pins 17-20: PWM, PWM, PWM, PWM
What is Pin 13? Is it a plain digital I/O pin?