Yes, I can confirm that something is happening. In google Argentina, google Mexico results have gone down.
I'm tracking all my keywords in almost all search engines, and at 3:00AM GMT +1 of saturday, almost all my keywords drop down 20 - 30 positions, and the long tails without links drop down 140 positions or more.
After one day some keywords return losing some positions and others one didn't have returned yet.
The "update/panda/penguin/..." has been done at 3:00AM GMT +1 of Saturday night.
My main search engine google spain, also have some fluctuactions but not too much strong.
Anyone knows something?