jay5r - 8:19 pm on Mar 9, 2013 (gmt 0)
Something definitely happened and I can say with certainty that whatever it was got rolled out between 6 and 10am on the 6th (Eastern time). I have a bunch of sites - mostly Wordpress blogs, but there's also a vBulletin-based forum in the mix.
One of the blogs is written in Spanish (on a .es domain) and it has a long history of being loved and hated by Google. It's up one minute with great traffic and then almost nothing the next. I think some of the trouble Google has with the blog is that many of the inbound links are from English language sites. Anyway, Google traffic to that blog went from about 3200-3500 new visits a day down to about 160-170 new visits a day - so it lost 95% of it's traffic. And when I look hourly on the 6th - it's a straight line down from 6am to 10am.
The other blogs (and the forum) didn't see any noticeable change to their Google organic traffic.