PPC_Chris - 3:51 pm on Jun 8, 2011 (gmt 0)
My guess is that Google could run this new Panda algorithm at any time, which would effectively lift penalties (or the penalty-like element of Panda) for sites that have been hit. But they are choosing to wait a few months. This gives webmasters enough to time figure out what Google doesn't like about their site and to fix it.
Also, Google wants to stop sites from doing similar things in the future and laying the smackdown to sites for a few months sends a clear message to clean it up and keep it clean. If a site was doing something that Google considers an intentional effort to manipulate their search results, the best way to stop this behavior is to penalize the sites. If all a webmaster needed to do to get their penalty lifted was get rid of the manipulative behavior and they instantly would be back, what is the incentive to not try something similar in the future? Its like SEO moral hazard.