Yahoo Answers is my highest traffic source next to Google. Thankfully the section pertaining to my website is very active, and those visitors tend to love ads as well.
In addition to leaving my url in the source box at YA, I also link to specific pages of my site in the body of my answer, when appropriate. I always provide very helpful information and make sure the links back to my site are relevant and provide useful info.
It has turned out to be a great source of traffic for my site.