A WebmasterWorld thread plus dozens of threads at the Google Webmaster Help forums have webmasters complaining about both ranking changes and traffic drops from Google's search engine.
The traffic drop would make sense being that it is a holiday and on US holidays traffic normally drops. But ranking changes cannot really be explained by an algorithm change.
Maybe all the black friday deals and all those new pages trying to compete on top selling product categories are popping up and Google needs to rank them properly? I am not sure.
One webmaster said, "I'm seeing what looks like a rollback today. Many verticals have returned to their former positions."
Another said, "We've been hit again, main keywords dropping even further."
Some can't figure it out if it is ranking or traffic.
Google has said they won't update major algorithms again during the Christmas holiday shopping season but who knows.
The Google tracking tools are not yet updated, with the exception of Algoroo but I'll keep checking Mozcast, SERPs.com and SERP Metrics to see if they agree. Update, it seems as if the tools do not agree.
Forum discussion at WebmasterWorld.