You know what I would
want my phone to be doing? To be
actually always listening. So that I could just say "Ok Google" at random and interact with Google Now without having to unlock the phone or have it constantly hooked up to a charger. That very simple thing would probably quadruple the usefulness of the whole thing. But Google probably has some "smart" reason for never ever allowing that.
sigh(I mean, what the hell - deep in the options of Google Now I can actually allow the phone to be unlocked by my voice - but if and only if it is plugged to a charger. They had to explicitly code in a special condition to make Google Now less useful.)
(and yes, I know you meant other kind of "always listening")