Duplicate Content Penalties
First let me start out by drawing a line here and define duplicate content in the context of this post: Duplicate content is content which other websites have utilized scapers or other means to take information found elsewhere and place it on other websites. It is also (more importantly in my opinion) content on your own domain that is available via more than one url.
For example, you can reach the content on this very blog via a number of avenues…through the homepage (temporarily), through the category specific page (which house the articles within that category), through the actual post page itself, and so on.
Having duplicate content (cross-domain) is of course frowned upon by Google due to the possibility to monetize someone else’s work or simply for blatant spamming and increasing your SERPs. On domain duplicate content is also frowned upon due to a number of potential exploitations.
So is duplicate content a major issue? Well as Sven of the Search Quality Team states:
I’d like to point out that in the majority of cases, having duplicate content does not have negative effects on your site’s presence in the Google index. It simply gets filtered out.
So that should tell us definitively it’s not a major issue right? Well, no. As we all know, SEO is a numbers game. We deal with small bits of optimization techniques that once pulled together gives you the advantage over your competition. Having duplicate content is not only not going to help you with that fight but if deemed done for ’shady’ reasons it can get you penalized and the penalties may be severe.
Here is the referenced blog posting about duplicate content from scrapers.