Wilburforce - 9:35 pm on Dec 3, 2012 (gmt 0)
Traffic way, way down across many sites from 50% to 80%
I only have a single site, so my own experience is obviously not widely representative.
My traffic is marginally up from last Monday, and from the same week a year ago (UK service sector). Google referrals are not much different either, even though this time a year ago my Home page was #3 for key two-word search term and it is now on page 72 (having crawled back to page 5 since last April, and then dropped 67 pages on Friday night).
What I don't get is why my Home page is getting penalised for that term and only that term (it is fine for e.g. <Industry Subsection Key Term> when it obviously isn't over-optimised, doesn't have a single backlink for only that term and only 5, all from reputable sources, that include it at all (I did a major clean-up earlier in the year).
I thought its gradual recovery for that term would continue. This sudden massive drop - exactly what happened in April - is unfathomable. The current #1 site - with a mass of self-placed backlinks that include pretty much everything from from air-conditioning forums to zoo-lover blogs - has not moved in 12 months (I can only think that such an eclectic and irrelevant set of backlink sources somehow gets under G's radar).
As rational explanations go, increasing dementia is about the best of them. I'm stuck for anything better.