Google quality guidelines were leaked a few months ago. Now Google shows examples of websites, which are removed from its search results, live. Look at those sites and if you have any site like this, delete it, before your site get a penalty.
The screen shots are generated manually, but they real example spam, as you can see, no one needs those sites. Google fights this kind of spam through a combination of algorithms and manual review.
According to Google most of these pages are generated automatically and scrap content from other sites.
Google also fights these types of spam
Here are some examples.