Overcoming Google Penalties
What does it mean to be penalized by Google? If Google believes that you are guilty of so called "black hat" SEO behavior then your site may be penalized. A penalized site will virtually disappear from all search engine results because Google essentially wipes all indexing history for the site. This is basically the worst thing that can happen to any webmaster and the best way to avoid it is to steer clear of questionable SEO behavior. Spammy content, paid link exchanges, etc. - these will all potentially get your site penalized by the search engines.
So how long does it take for a site to be forgiven? Some say that a year is the standard and that's only if you immediately end the behavior that got you penalized and promptly request that your site be reinstated.
To preserve all of your hard work, the best plan of action is to avoid at all costs getting penalized in the first place.