A part from the story, the internal ethical struggles of a man very good at his job, angst of a broken family, conniving ways to get truth, and the negative effects smoking has on your body, Thank You For Smoking was a hilarious look at PR. The main lesson I take away from it is that it's not so important that you're right, but that the other person is wrong. OucH! It reminds me of McNamara's advice (and lesson) from his term as Secretary of Defense: "answer the question you wish you were asked."
The film also hopefully makes an obvious jab at smokers (not all granted!) that anti-smoking campaigns aren't so much about stopping you from smoking, just not smoking around, well, non-smokers.