The links from Yahoo Answers have absolutely no link value. In terms of ranking in Google it sucks! Every link has a nofollow tag, which makes it kind of useless.
its really sucks.... i joined it to promote my blog, but i didn't post my blogs link until i was on level two(you have to give 100+ answers for that), after that i posted my link to two to three answers and they just banned me how ridiculous... i think these forums are good, but they have become a bit strict too.....