Google released the Panda update number 21 on November 5th, 2012 which affected around 1.1% of English queries. The news was revealed through a tweet as displayed below:-
Here is what Google recommends to read about Panda:- Finding more high quality sites in search.
Impact
This update has affected 0.4% queries worldwide. Some webmasters have experienced a recent drop in the rankings while others have experienced an increase.
Also See:-
Google Panda Update Number 20
Google Panda 3.9.1
New Google Search Quality Updates
EMD Update
Google Penguin Update
Google Human Quality Raters Do Not Influence a Website Rankings Directly
Nice Blog !!