As an industry, our position on what makes a quality link has changed over the years, specifically in the past year, and most tactics have followed suit. This shifting paradigm can easily be attributed to the Panda and Penguin updates and refreshes, which have placed a strong emphasis on valuable content and natural, quality link signals.
With this push towards the complete removal of manipulative practices, in addition to scare tactics on any form of guest posting, SEOs are left with a smaller tool set of tactics that work to produce link signals that are beneficial to a site.
In short, the gap between the links that actually work to increase authority and what Google says works is closing. And, if updates continue on this track, those opting for quick and easy links are going to find themselves in trouble.