Don’t forget that real-time Penguin is inherently very granular in this
regard.
But, it’s important to note – not all guideline violations will result in
penalties.
Some result in issues with crawling and indexing, which can also
impact your ranking.
Others result in major manual actions, such as spammy links back
to your site.
When a manual action hits, it’s important to remain calm.
You have likely brought this on yourself through link spam or
another type of spam on your site.
The best you can do now is investigate and work with Google to
remove the manual action.
In general, if you have spent a lot of time getting into trouble, Google
expects the same amount of time to get out of trouble before you
get back in their good graces.
Other times, the site’s so terrible, that the only solution is to nuke it
and start over.
GOOGLE WEBMASTER GUIDELINES: EVERYTHING YOU NEED TO
KNOW & UNDERSTAND