I am a bit torn, I've seen some chatter over the weekend at both WebmasterWorld and Google Webmaster Help but not enough to see strong signs of a definite update, like the one we had with the softer Panda update about ten days ago.
But I am also seeing signs from some of the SERP tracking tools of an update. For example, MozCast showed very high changes with 105 degrees on Friday but cooler weather on Saturday. Whereas, SERPs.com showed very high volatility on Saturday, not Friday. SERP Metrics is all over the place, while Algoroo is showing high changes both Saturday and Sunday but lower activity on Friday.
To me, this seems like one of those limited updates where Google may have not made a huge algorithm change but rather there was a change with either some link network or maybe a UI change causing this.
I am not sure. I wanted to see what you had to say about this and if you think I should bug Google to go on record about this possible Google update.
Here is one message in WebmasterWorld:
One of my major site got hit for roughly 15~20% of traffic. It started on Thursday night time (Friday?) and continued to drop off until today. I am not sure if it's simply the summer vacation is coming to an end or if I am getting more competition in my space.