Google Penguin struck in a big way that made SEO news when they crashed a wedding site that was allegedly using some black hat, or at least shady, link building strategies and tactics. What Google deemed as a problem is well worth noting as this was a strategy that used to work to a degree, but was never really considered all that legitimate by some SEOs. It involves two aspects of site management that should be avoided at all costs whether Penguin existed or not – low quality content and unnatural links.
What they did was leak out low quality content to poor reputation sites with links pointing back to their site along with money keywords that were only linked back to their site. The problem was threefold – the content was substandard. The links were unnatural, and the link building took place in bulk at regular intervals. This all pointed to non-organic growth. When Google sees this and they can easily identify content that exists for no purpose but driving links juice and is of no use to actual people, they strike fast and hard.
It is a hard lesson to learn and almost impossible to recover from. Google is letting people know they are serious about making sure content is useful to readers and that links exist in a manner to enhance that content and not for the sole purpose of driving link juice. We can espect to hear of more examples of this as Penguin is more fine tuned than at launch and getting to many sites that slid by the first waves of analysis.