It took me a year of membership and 9000 points rep to learn that you are notified about new answers if you make a question a favorite. And I learnt it just by chance: Someone mentioned that in a comment.
I am sure that is explained somewhere. I didn't look that up now because it doesn't have any effect on my history here.
I suggest modifying the fly-over help for the favorite button. It should not just tell that this make the question a favorite but that you are notified about new answers. I consider that an easy and probably effective change.