This is what I know:
kernel provides info through /proc/apm
apm allows you to read this in a nicely formatted manner (but provides no more info).
apmd sits there and looks at /proc/apm waiting for events to occur.
Now my question is what does the light & power applet actually change? I presume there must be a config file somewhere which is written to by this applet (and it's not the same one as is passed to apmd afaik).
Also, apmd just sits there waiting for the events, what actually times inactivity and then decides to suspend/turn down backlight/etc.?
I'm after this info as I'd like to improve power management on the pdaXrom.