To be perfectly honest with you, if I were to market something smartly, I would probably use a culmination of both Yahoo Answers and ChaCha. With Yahoo Answers, it is easy for your answer to be flagged if you aren't careful about the phrasing and content of the ones you post, regardless of your level, although a higher level will tend to discourage sabotaging people from flagging them. On the other hand, like the users above me have said, the site ranks much higher and is vastly more popular than ChaCha, meaning that the effort you put into posting your links may garner a much better return on traffic in any period of time. Also, Yahoo Answers is very community oriented, meaning it is indeed possible to establish your site as an authority on a particular topic or niche, whereas it may not be as possible with ChaCha. Unless you were to, say, comment the same link on a variety of the same type of questions. The risk of getting flagged is greater with this, however.
I wouldn't shun ChaCha altogether, though, as people tend to post some very targeted questions there for a random visitor to find, too.
All in all, the clear winner is Yahoo Answers as the best traffic source.