Last year on July 27, Google released a blog post mentioning about New Notifications about Inbound Links. Basically, Google started sending un-natural link messages via Webmaster Tools to sites that were potentially getting links from spammy or artificial sources.
A major percentage of sites receiving this message noticed a sudden drop in rankings thereby affecting site traffic and impressions.
On Monday 15th July 2013, we have seen improvement in the rankings for few such websites which were hit by unnatural links last year. Apart from rankings, the impressions for the site have also improved. Below is the screenshot from Webmaster Tools of one such website. Hopefully more sites have been released from their penalties!