A few things that could cause an over optimization penalty?

I read a good article that explains a few things that could cause an over optimization penalty, the following are the summary of the article.


What could cause an over optimization penalty:
  • Keyword stuffing
  • Redirect several domains to one site
  • Same / similar anchor in backlinks
  • Same Niche same server
  • Doorway / thin affiliate
  • Link schemes / cheap backlink packages