There are quite a few penalties flying around that you may not even know about. For some on Word Press you need to be sure that you tone down some of the SEO related plugins. For many sites G has added page rank adjustments based on what it thinks are bad practices, they can ban a site de-index it, create a penalty or filter and you may not even know it.
This article will help you find out if your site has a penalty etc and offers advise on how to fix it. Its a valuable resources when the gateway to the internet become the Gatekeeper! I cover that idea in my book on how to market any business on the internet.
A G penalty for spammy SEO or bad quality on site is often referred to as a Google Slap. However a SLAP is really a penalty that applies to advertisers using Adwords – see more on the Ad Slap here >>>>>