While Google will probably never admit to it, the post-Bourbon adjustments appear to have been largely driven by human reivew. Most affected have been sites that experienced big drops or gains during the Allegra and Bourbon algo updates. In all likelyhood there is now an algo that's flagging borderline sites for human review and, in some cases, applying a temporary penality.
Sorry but I had to laugh when I read that. They don't even listen to reports of blatant spam repeatedly sent to them affecting huge key terms and you believe that? Tell you what, find a spammer, the most egregious spammer you can find. Report them to Google and I say you can't knock them out of the index no matter how hard you blow. Shame on Google I say.