I could get a 16MHz 5V Arduino down to approx 1uA.
If you could get the avr to run on a 16Mhz crystal with less than 1ua, you should contact Atmel, 
Getting an avr to run below 50ua is easy, even on a crystal. Getting it to run below 10ua on a crystal is difficult. Getting it to run below 1ua on a crystal is out of this world.