This thread is interesting, these are my thoughts on some of the examples that have come up.
I think the question "how are you" is meant to lubricate social interactions, and not be an opening to tell someone the story of your life. I think good, busy, not too bad, how about you, are all normal responses and don't need to be analyzed or considered lies. But if your spouse or family asks you because they truly want to know, going into depth is appropriate.
I don't really see the point of lying to someone about how they look, you aren't doing them any favours and usually if I ask that question I would like an honest (but tactful) response. But don't ask the question if you can't accept the truth. Also, don't make insincere compliments, if you have nothing nice to say, just don't say anything.
Breaking the law and stealing are usually unethical, but accidentally swiping a pen isn't really stealing. It would only cross a line if you regularly and purposely did it so that you'd never have to buy your own pens or something.
And breaking the law is not necessarily unethical, if the law itself is immoral. If there's a law against homosexuality, it's not unethical to get married as a gay person, but the law itself is what needs changing. If it's illegal to protest, but injustice is occurring, it's practically your duty to protest it.
To me, the line on ethics is where the action crosses from harmless to harmful, and from inconsequential to consequential. Lying to your kids about Santa Claus is pretty harmless and inconsequential, up to a certain point, but I'd never bother to lie once they started to figure it out and question it. Lying on a job application is definitely consequential and therefore unethical.
I'm a bit torn on music or movie downloads, cause on the one hand the artists aren't getting paid, but I only feel bad for small time artists, not people who get paid millions. And most of the time, it's not depriving them of a sale, if I can't download it I just won't watch it, I wouldn't have bought it anyway. Maybe I am a bit unethical on that point, but I consider it fairly inconsequential and not that harmful so it doesn't cross my personal line.
Finally, credit card bonuses exist to be used, and if they didn't want you to have them they wouldn't offer them. For credit card companies I'm probably the worst customer, I never pay interest and I usually just fulfill the minimum conditions to get the bonus. But it's not my fault if they lose money on it, I never lie to get a card and I think they weigh the cost of people like me against the real clients they expect to get and consider it the cost of doing business or the cost of customer acquisition.