I read that a few months back; very well written, I'd like to see the guy do more! If we're not hung up on using the "pin 13" LED, then a timer can do the blinking for us with no additional code once it's set up:
//Turns an LED connected to Arduino pin 9 on for one second,
//then off for one second, repeatedly. Uses Timer/Counter1 to divide the 16MHz clock
//by 256 with the prescaler (to 62500 Hz) and then toggles the pin after
//62500 counts (i.e. 0 to 62499).
//
//478 bytes with Arduino 0022
void setup(void) {
DDRB = _BV(DDB1); //set OC1A/PB1 as output (Arduino pin D9, DIP pin 15)
TCCR1A = _BV(COM1A0); //toggle OC1A on compare match
OCR1A = 62499; //top value for counter
TCCR1B = _BV(WGM12) | _BV(CS12); //CTC mode, prescaler clock/256
}
void loop(void) {
}