An update to Google's search index arrived prior to the long holiday weekend here in the U.S.
Google's Matt Cutts announced the "data refresh" on Twitter late Friday afternoon. Despite claims otherwise, this is the first official update since the "Penguin" update rolled out in late April 2012. Many SEOs noticed shifts in the SERPs throughout the month of May which were likely just live tests of this current update.
Penguin, an algorithm change that took direct aim at sites that were violating Google's quality guidelines, has caused quite a bit of digital commotion in the past month. This most recent update, now being dubbed Penguin 1.1, refreshes the index based on changes Google made since Penguin arrived. Cutts indicated in his tweet that less than one-tenth of a percent of English-language searches would be affected.
If you were negatively affected by the initial rollout of Penguin, the good news is that sites that were previously penalized (perhaps mistakenly) may see their sites return or recover. The bad news is that it's likely not over yet – Google will likely roll out numerous updates to Penguin over the course of the next few months. Those that believe they escaped a Penguin penalty initially may now lose their positions as Google refreshes its index based on improved/modified filters.
So what should you do? Stay calm, geek on, and watch your ranking positions closely over the course of the next week.