In the past 20 hours or so, I have seen a huge uptick in the number of complaints in the Google Webmaster Help forums with people complaining that their sites no longer rank in Google.
Update: This is not the "over optimization" penalty as we thought. Matt Cutts posted on Google+ it is related to a "classifier for parked domains" which went haywire. Google fixed the issue, Matt said:
I saw a recent post where several sites were asking about their search rankings. The short explanation is that it turns out that our classifier for parked domains was reading from a couple files which mistakenly were empty. As a result, we classified some sites as parked when they weren't.
I apologize for this; it looks like the issue is fixed now, and we'll look into how to prevent this from happening again.
So I guess we are still on a holding pattern for the over optimization penalty.
Here is the rest of the post as it was...
I captured 11 different complaint threads before stopping, I suspect there are about 25 or more complaint threads and many many more webmasters suffering from a possible Google update. Here are some of those 11 threads; #1, #2, #3, #4, #5, #6, #7, #8, #9, #10, #11 and many more.
The ongoing WebmasterWorld thread has taken notice of this as well. One said:
Our niche has been heavy shaked up. Most of the upcoming ecom sites are low quality - > I think it has somthing to do with the "overoptimzed" and "level" efforts, cause this shops only have little ranges and will not hit the SEO overoptimized barrier.
Did you notice major changes in the search results?
Forum discussion at Google Webmaster Help.