Yahoo Answers are nofollow, which means no link juice passed. But it might affect SERP still in terms of relevancy scores for keywords? Plus Yahoo answers brings in some good traffic. Also, not all search engine care about no follow, some of the older smaller search engines will still count those links.
Links in Yahoo Answers are nofollow, but the traffic you can generate from posting it is tremendous, esp. if your answer has been tagged as the best one.
Yahoo Answers is definitely no follow. Although you can get some traffic is your answer is selected as "Best answer".
Yahoo answers are nofollow but gud ones they are a strong link to have. You can grab lots traffic not that much but you can get good traffic from it if you write good answers.
The no follow links gains no result in search engines rankings but it helps to drive traffic to the site.
Page rank is not all. Domain trust is a VERY important factor too. So don't exclude you tube, Wikipedia etc.