A minute ago I was asked in a PM why I do not recommend article submission as an SEO tactic.
First off, article submission may be useful, not for SEO, but for website promotion, if those articles are submitted to high traffic sites that actually drive traffic.
However, most article submission services and article submission directories are simply spamfests. They accept any odd rubbish, and then websites owners, hundreds of them, place those rubbish articles on their rubbish sites in an lame attempt to pick up "
long tail" keyword searches.
However, some article submission does drive traffic. For example, submit a high quality article to SEOToday and it might drive some traffic. But then, the selectivity is there, and 99% of rubbish submitted will get rejected. That makes a huge difference.
The other you have to ask is, if you have a high quality article, why give away that content for free? You should think about putting it on your own site and reap the benefits - links and traffic.
Now, on to uniqueness and the supplemental index. First:
Source: Internet Marketing Blog.com
Google is going after duplicate content, and placing it in their supplemental index, in order to diminish / block the passing of link juice from spammy duplicate content.
Duplicate content, such as article submission spam and automated web directory submissions (
which use the same description & title for hundreds of directories), has been used for years by SEO's and these are the same SEO's who are now complaining about lost rankings.
Supplemental index = duplicate content = no link juice.
Article submission for SEO is just another form of spam. Google knows it, and has reacted.