"To give you an idea where we are with power, consider the little green LED that blinks whenever you've got a data connection. On a device I was working on recently, I increased the total device standby time by 12% by reducing the amount of time the green LED was on from 200 milliseconds to 50. We're talking about almost a day of standby time here. " NOR, NAND and XIP http://blogs.msdn.com/windowsmobile/archive/2006/06/19/637638.aspx
That's for a PDA. I'm now going to go look for a registry key that lets me set that LED! I'm thinking about battery technology for a feature I'm writing; we're getting further with evolutionary sensible optimisation than we are with revolutionary new chemistry.