#4 Duplicate Content
The particulars of the Duplicate Content Penalty are fuzzy, but the big picture is clear. Matt Cutts and company have flatly stated that duplicate content can negatively impact Page Rank. The question for SEOs then is, “What exactly is duplicate content?”
For the most part, you won’t be penalized for having the same text in several places on your site, so long as your using canonical links. The problem comes when you’ve got the same story in three places without explanation. Google bots will read it as only one story and you could get penalized for not having enough content (when measured by percentage).