Google plans to penalize overly optimized sites because they want to level the playing field for other websites who do not concentrate on such efforts. Basically there are sites out there that completely focus their efforts on SEO and not content and those results would rank higher than sites that don’t focus on SEO.
Google Engineer Matt Cutts explains the following: “We are trying to make GoogleBot smarter, make our relevance better, and we are also looking for those who abuse it, like too many keywords on a page, or exchange way too many links or go well beyond what you normally expect.”
The search engine at Google is about to go through a major overhaul and de-prioritizing sites with heavy SEO is just a small part in the big picture to bring better search results. The changes to the search engine will be coming in the next few months.
Now I can see two separate arguments on this matter, the people who spent a lot of time on SEO and the people who did not. Honestly from what I have seen from results on Google I am all for this change because I am tired of finding results for sites that make no sense for what I have searched for. The people who spent a lot of time on SEO will likely not enjoy this change but most of those people have taken to link exchanges and keyword spamming on their blogs and sites. This change will help sites that may not understand the SEO game but have great content, so I look forward to better results. Who knows exactly what Google will be looking for.