We've been watching the Google "minus thirty" penalty for quite some time. Recent reports at WebmasterWorld have webmasters relying upon each other for support and advice, and after several months, some people have lately been successful.
Some people admitted to having duplicate content. Others feel that it's due to participation in link schemes and having sites linked to bad neighborhoods. Even others feel that their pages may have been over-optimized. In some cases, paid links were removed. It also helped numerous webmasters to clean up the code.
After reevaluating the site, ensuring there are proper 301 redirects, and editing the robots.txt so that it would not be spidering any duplicate pages, many have had a lot of success after submitting a reinclusion request.
Forum discussion continues at WebmasterWorld.