Google is really pushing for link building to become more about link earning. The new attitude centers around the diea that if you wrote a guest blog post then you put the link in there, meaning it’s not an editorial “up vote;” it was a pre-planned link. In the Webmaster Guidelines Google’s John Mueller states;
Generally speaking, if you’re submitting articles for your website, or your clients’ websites and you’re including links to those websites there, then that’s probably something I’d nofollow because those aren’t essentially natural links from that website.
Should you get quoted or referenced in a post on another site (one that you did not write yourself) then that link can be followed since it is a naturally earned link.