"Penguin has now been reverse engineered. The results are shared including what is likely wrong and what you can do to fix it.

This is totally different than what most of the SEO world is telling you to do these days."

(Source: http://www.senuke.com/blog/?p=276)

Josh Bachynski reports in this video that the biggest surprise for most people will be the fact that Penguin has NOTHING to do with your backlinks, as it only targets on-page factors.

Key take-aways from the video:

1) You need to fix on-page issues as the top priority

2) Penguin-based negative SEO is not possible

3) No need to delete links - Google is already taking care of that by devaluing those

4) Add quality links to your key content in ways that make them look "natural" to Google (30% exact match query, 30% partial match, 30% url-based, 10% generic/other stuff)

5) Do not overoptimize - Google knows what your page is about - don't overdo it with keywords. Check with Google Webmaster Tools and see what Google thinks your page is about.

6) Try always to look and be as "natural" as you can be. 

Must see. 9/10

Watch the video for a complete explanation: http://vimeo.com/42939368 

(Thanks to Nicoleta Leon for pointing me to this)