[xja]

The article mentions microcontrollers that use 100 milliwatts as the lower end of embedded CPUs.

There are actually microcontrollers that use around 1milliwatt for very low power applications. For example the msp430. TI have a neat video of one running using power generated from grapes:

https://youtu.be/nPZISRQAQpw

[david-given]

Last time this came up someone pointed me at the new generation of ultra-low-power ARMs:

http://www.atmel.com/products/microcontrollers/arm/sam-l.asp...

35µA/MHz, so with careful selection of peripherals you probably don't even need a whole milliamp.

[sbierwagen]

Designing microamp-level systems can be interesting. From http://www.ganssle.com/rants/leaks_and_drains.html :

  I put one of the boards under a microscope and looked at 
  some of the ancillary parts. There's a 22 uF decoupling 
  capacitor. No real surprise there. It appears to be one of 
  those nice Kemet polymer tantalums designed for high-density 
  SMT applications.
  
  The datasheet pegs the cap's internal leakage at 22 uA. That 
  means the capacitor draws a thousand times more power than 
  the dozing CPU.

[dbcurtis]

Yes, I play with little robots built with microcomtrollers. For some of our little boards my friends and I make we leave off the LEDs because they consume more battery than the CPU. (Of course the motor makes up for that quickly...)