I give the "fine, thanks" to someone who doesn't really honestly ask me how I'm doing and only does so for the sake of formality. They don't honestly want to know how I'm doing. They don't want to hear how my dog just died and my boyfriend just broke up with me and how I'm late on my car payment. They just want to hear that "fine, thanks."
Honest questions evoke honest answers. Truth shouldn't be denied when it is sought, regardless of the consequences.
Yeah but... I know the considerate reaction is simply to say, "Fine. And you?" But I just can't bring myself to do it. "How are you doing?" does not seem, to me, like a rhetorical question. If you don't want to know how I'm doing, then don't ask me. If you simply want to convey friendly greeting, then nod, smile, mumble "howdy", make a peace sign (or "live long and prosper" or "whatever"), but don't ask me such a question if you don't want an answer. Because you will get an answer. And the more apathetic or annoyed you seem, the longer that answer will drone on and on and on and...
Regarding "white lies", in my youth (paleozoic era) the art of "white lies" was part of "good manners" (not just a canon of rules, but genuine consideration of others). The basic question we were taught to consider was this: is the other person in a position to change his actions based on your "honest" answer, or will he just feel badly, perhaps even function less well? If the other person has a choice of actions or options which your answer may affect, then it is disrespectful not to be honest with him. But every situation is different, so in the end it boils down to your best judgment call.