I found this article to be really helpful: http://www.positivediscipline.com/articles/lying.html

It is really intended for parents of older children but it may give you some things to think about in the future.

Personally, I do not think it is a good idea to make a big deal out of the sorts of situations you are mentioning. His behavior in the first situation suggests it may be helpful to back off from discussions of being a good or bad boy and just to focus instead on telling him more specifically what you want from him. When situations are set up that kids anticipate punishment they are more likely to lie.

As far as the last situation, I would see that just as social politeness. We often smile when don't want to be rude and we are trying to negotiate a situation in a way that won't hurt another people's feelings. If anything I would praise his behavior as attempting to be considerate.