It isn't as easy as that.
Before "Penguin" update Google released 40 and after that 50 different updates, targeting many things, but the most significant one was related to link evaluation algorithm.
One of those 90 updates was targeting over-optimization filter, however this wasn't the main reason for rankings drop, but error in algorithm.
Right after this error in algorithm so called "Penguin" update was released.
The best source to check information is not on blogs and forums, but Google webmaster central. Honestly I have when bloggers are throwing tons of misleading information without even have a clue about SEO.
Even official Google statements are misread often and only experienced SEO with more than 5 years of experience usually know what is all about.