Oh, I didn't realize that. Will it interfere with my circuit if I'm running from a 5V regulator and I'm not using the analog pins? The standalone page on the arduino:
shows AREF going to +5V (though each of the pins does not have its own 0.1 uF as you noted).
What do you mean by 'SCK'? I'm testing the digital out on Pin 13 (Pin 19 on the chip) with oscilloscope probes and getting nothing; using the same technique on the UNO I'm seeing the square wave output.