This guy got penalized by Google. He made some adjustments and got in touch with Google to let them know. This is how his traffic gradually climbed back:
Below is the graph of how the Google penalty played out. I wasn’t surprised by the 90-day duration of the penalty: I had read other reports of similar link-based actions. I didn’t expect, however, the gradual ramp-back of the the “penalty release” period. In all, it took about 4 months to get back to normal traffic.