My site (informational) traffic also went down on April 15. Since then it has been very strange. Today is the worst day since 2011. I do update my content on daily basis. I have a professional writer who write very detailed and specific content for our site and visitors think our website is one of the best for our topic. We get tons of compliments from our visitors. The site used to grow steadily in traffic since 2004. We have backlineks from CNN, FoxNews and other big sites (we never asked for these links, they just mentioned our site in their articles). So what I am observing since 4/15 is very unexplainable for me. We are very "White Hat" SEO oriented and we dont buy links. We get links from Facebook, Yelp, Wikipidia and many other sources but this is how Google wants it right? - people to link to you because they like your website. Then why is our traffic down since 4/15?!