It does not take an Online Search consultant to know about the on going issues with duplicate content. Everybody should be well aware that the major search engines love unique content. Search engine filters were brought into place by the major search engines and ever since it has become something of a harmful topic.
The problem arises when you do not understand what duplicate content is as it means more than an identical page on your site. I have been an Online Search consultant for 3 years and at least 30 percent of my clients have had issues with duplicate content so it seems not everyone is aware of the concept.
In its basic terms duplicate content means any page on or off your site that is identical or similar in content. It does not have to be identical as long as it is appreciably similar. There are harmful types of duplicate content and harmless. Harmless types of content include discussion forums, product pages and print only pages. The harmful types of duplicate content are those specifically designed to manipulate search engines and confuse indexing.
This is why big search engines such as Google hate duplicate content, they want to give you the most relevant content at the top of their SERPs, but which pages do they use if there are 100 pages that are identical or similar. It is for this reason filters are used, if your page is identical to another page either on your site or else where on the web, it will simply index the page with the most authority.
There are some simple things to avoid in order to prevent search engine penalties. Do not steal content, as well as an obvious Online Search effect you could also find yourself in trouble with copyright laws. Check for scrapers, these are people who are using content from your site to populate pages on their own. A good tool to use is copyscape. If you find anyone copying your content email the webmaster and ask them to remove it and also file a complaint with Google, Yahoo and MSN.
If you run more than one site based on a single theme ensure you create distinct content, this also applies if you have identical sites in different countries. If you run an affiliate site or online store, try to create unique reviews and product information, this will prevent your content becoming mingled with other product specs on the web
As an Online Search consultant duplicate content is one of the first things to consider when deciding the file structure of your site. If you follow the above advice and make a real effort to produce unique content you are very unlikely to be penalised by the major search engines.