Hello, the code in the built-in example file (examples/leds/led_drivers/max7219_v1) and the playground file http://www.arduino.cc/playground/LEDMatrix/Max7219 have bugs in them. As it so happens, the code will still work with a 7219 but not with an identical, fully SPI-compatible chip like the 7221.
In the max7219_put function, the load line should be set LOW to begin, not HIGH. this is not strictly necessary for the 7219, only the 7221. But it is technically wrong regardless. ["For the MAX7219, serial data ... is shifted ... with each rising edge of CLK regardless of the state of LOAD. For the MAX7221, CS [LOAD] must be low to clock data in or out."]
void max7219_put(byte reg, byte data)
max7219_setLoad(LOW); // begin ** in the example this is HIGH, which is wrong! **
max7219_putByte(reg); // specify register
max7219_putByte(data); // put data
max7219_setLoad(LOW); // latch in data
max7219_setLoad(HIGH); // end