Mario, You are correct, sir. Had the same thing happen with two of my client's sites over the past week. Traffic fell by 40% in one day, keyphrases that we were always in the Top 10 in did not even show in the top 50 etc etc etc. And it is still going on. Page Rank was not really affected, but traffic most surely was. I'll be glad when Google goes the way of IBM OS/2.
What's interesting is that for one keyphrase my main url that used to be top 10 - www.domain.com - does not even show up in the top 100 but an internal page has replaced it on about page 6-7 of the results...meanwhile for another search phrase my www.domain.com shows up rather than that internal page. Google is more complicated than a woman.
Is that even possible? OTOH, all we can hope for at this point is for this to shakeout by the weekend or so.
traffic has fallen for my site too.. nearly half of the traffic it used to get before from google.. however the rankings have improved on certain popular terms but don't knw why page views have decreased.
You will find thousands of pages "duplicating" your content searching fro separate phrases for your site. English language has fixed structure of sentense, thus there MUST be many instances of sentenses built using same words and same structure over the internet. There's nothing to worry about.