We did a soft launch of the new site and really took it live in December of 2011, so that is the bump you are seeing there.
The Penguin hit was sharp and instant on April 24th. Not sure precisely when the clean out was done. We have an off-site SEO who handles that. I was told that it was pretty much one bad link that had replicated across a a slew of blog postings and has since been cleaned up.
The 301 redirects were done more recently, in August. It took us a while to figure out that that was part of the problem. Some of the redirects have worked perfectly. The new site replaced the old site in the SERPS with almost no change in ranking. Others fell off a cliff. All the content and tags were relatively consistent across the pages that had the redirects applied. It just seems like we've got two separate groupings here. One has recovered from Penguin and the redirects have worked and the others we just can't get fixed.
At no point in any of this have we received any notifications from WMT.
Thanks!
Doug