I was just playing with the power button this morning. A long press will turn it on/off, but it defaults to on (it comes on automatically when power is applied).
I don't see any effect of sleep mode. If I press the power button for a short time it doesn't seem to have any effect.
I'm also wondering if/how the power button is programmable. I would like to have the Edison remain powered off when it's powered (or turn off as soon as possible) if that's possible, and require a long press (ideally shorter than what it's set at now) to turn on.
I have seen in a different thread that the power button was not programmable.
Although, for the extremely advanced and certainly at ones own risk, I noticed the pwr_button_handler located in the /usr/bin directory runs as a process which means it most likely could be replaced.
I have not personally seen any source code or specs defining this - probably leaning towards a fact that we shouldn't.