n00b1 - 4:35 pm on Feb 21, 2012 (gmt 0)
Wokka, just to chime in here with some similar experiences. I experienced a similar and thus far explained drop for my main keywords on 08/12/2011. I still haven't seen any recovery nor have I received any indication from Google about what could be the cause (and if a manual penalty was indeed applied) after 3 reconsideration requests.
I have thought of many things that could have contributed to this and most are being cleaned up. Just little things like 'replytocom' and 'comment-page-1' pages and posts being indexed when they shouldn't be. The material is identical to the original post/page and will count as duplicate content - in my experience with these, parameters in Webmaster Central Tools and any canonical tags don't seem to fix the problems. So I have had to robots.txt these and am deleting any replytocoms or comment-page-1s that crop up in the index.
I don't even know if this will bare any fruit and I may be embarking up the wrong tree. I have also recently removed a number of older or 'thinner' posts on my website with blatent "you come here, you go to this site through this affiliate link" type promotions. These were a very small proportion of the overall site content but it seems that something tipped the balance back in December and I'm not quite sure what.
Regarding reconsideration requests, I received a reply within 2 weeks in both cases. I gave a third reconsideration request at the end of January (31st) and haven't received a reply yet. I don't like to have to send so many reconsideration requests in a relatively short period of time but it's partly Google's fault because the replies I have received so far are completely ambiguous:
"We received a request from a site owner to reconsider how we index the following site:
We've now reviewed your site. When we review a site, we check to see if it's in violation of our Webmaster Guidelines. If we don't find any problems, we'll reconsider our indexing of your site. If your site still doesn't appear in our search results, check our Help Center for steps you can take."