@Convergence - when did that happen? The date?
We saw a dramatic drop in traffic that many were reporting in the US starting in the afternoon of Feb 12th and lasting exactly one week; now UK site owners are reporting seeing the same thing in the time frame that an update usually takes to reach the UK SERPs, when it ends here it starts there. The last time I saw this behavior was in Nov 2013, the week BEFORE an announced Google update. I'm expecting an announcement soon. Barry Schwartz says no unannounced Penguin updates [searchengineland.com...] and there isn't really any indication outside of here about other updates.
I have to say that it seemed like an algo update at first but there was no level off or bounce back during that week, nothing but shortfalls. AdSense was paying horribly low EPC during that week as well. Over the last couple of days traffic is normal again starting Tuesday the 19th afternoon/night.
Can't say exactly what it was that caused it but will say that one of our sites that gets NO traffic from Google showed a similar behavior in the same time period and some others that do rank on Google showed no effects at all during that week. It almost seemed like it was EMD related, please read on....
In the SERPs we were surpassed (not buried) by both new and existing sites which explained the shortfall in traffic; 70% of those sites have one thing in common, I won't say what that one thing is but it can be seen right in the SERP without visiting the other sites. Another thing they had in common was domains that did not contain keywords at all, some with synonyms but not many.