By Google's own admission this will affect rankings:
"We can’t make a major improvement without affecting rankings for many sites. It has to be that some sites will go up and some will go down."So whats the main point of this change, besides Google doing the decent thing and serving up better more targeted content for users.
I believe that this is to promote and encourage content writers to create more quality and unique content. By phasing out content plagiarisers and giving decent rankings for content scrapers we should start to see original content writers being elevated to where they belong in SERPS.
Google have proven again why they are number one in the search space and once again that search engine rankings are never a certainty.
As far as Search Engine Optimisation (SEO) is concerned, we now wait patiently to see how our clients fair with this 1 in 10 change.
I personally believe that it is suicidal to be proactive with changes like this. Keep a close eye on your analytics and react.
There is a fine line between pioneer and martyr...
See the blog post here: Official Google Blog: Finding more high-quality sites in search