Yahoo Answers works for building up links I personally get about 70 + visitors a day to my cell phone site from it. It's easy to use too. Just search for the keyword you want to answer on and check the results for the ones that say " Open Questions " respond to the Question and post your website link as the resource. Works !
those back links are no-follow which means that as the question gets old and berried, less people will visit your site.
Normal yahoo answers are nofollow . But checkout wiki.answers.com ,ask a question and add related link . They are dofollow...