1. If I don't know you well I answer the question of how I am with fine, thank you. Once I know you well, I drop the thank you. Backwards, or at least half-rude, assuming you aren't actually interested is right or at least an acceptable theory, ("'how are you' is a greeting, not a question.") but I need to remember to be polite.
2. My friend used to answer completely honestly, every time. I'd ask her and she'd shake her brown hair -- Oh, really bad. Something about it made me smile later, remembering, no matter how tragic the following story, no matter the strife my poor friend had encountered at the grocery store just ten minutes before I saw her, that honesty was endearing, as was the assumption that I was interested.
3. I was, usually.
4. She still does this, but has a much happier life.