On 16th August 2012 A Google Ranking Change?
There is some yack going on at WebmasterWorld thread and then dozens and dozens of complaints in the Webmaster Help forums.
Now, this might be Google testing a fresh algorithm, or testing an update to an algorithm. Or it might be a heap number of individual sites received manual punishments. It can also be a bug with Google or even nothing at all. Time will tell.
Barry Schwartz see the Mozcast report for Thursday update later today. SERP Metrics doesn't indicate any major shifts from the norm.
Did you observe major ranking varies yesterday in to today?