On Feb 27th and 28th Google rolled out a fairly significant algorithm change that impacts a lot of websites and SEO. As discussed in a Softlayer interview that was posted on their partner page the impact on SEO results is significant.
This Google algorithm change What we were are seeing is that websites that were doing a lot of ill advised SEO e.g. blog networks, linking networks, etc were penalized. That is good for you if you were writing original content and utilizing guest blogging and other legitimate link building techniques. If you were taking short cuts and signing up for blog networks this Google algorithm change likely had a significant impact on your rankings.
Here is the official blog post from Google Algorithm Change .
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