Our site got affected by Panda between Jun 2011 and September 2011 when we lost 2/3rd of our traffic. Recovery efforts began only by Jan 2012 after I came in.
Our site is a Q&A site which publishes original threads as individual pages with related Q&A content. Google is quite happy with this. The problem was in "search results" pages that had long-tailed URLs and questions from our DB based on those long-tailed words. In these pages, we showed around 15 questions linked to their individual question pages. There were "quite a bit" of them, more than the number of actual Q&As. Panda (unsurprisingly) soundly thrashed them.
We have got 90% of our "search results" pages removed (404'd/410'd) in stages, starting January and the results generally, have been encouraging. Individual thread pages gained more traffic than that lost through "search page" removals. This was till Aug 26. Oh. We also publish thread pages daily as users post them and gain traffic every 15 days or so because of that.
In the 2nd week of August, the index of the "search results" pages started increasing and went up 4-fold though we did not add any pages. In the next week, the traffic in the "search results" pages went up by 15%. However, in the following weeks, all pages started receiving less traffic. The index remains around the 4-fold range. We checked (ad infinitum) to see if any extra "search results" pages have inadvertently been published. Looks water-tight. The only thing is that we increased the crawling rate around 20th Aug.
Some supporting information:
1. Index is close to a million (with the bloated "search results" index that makes 50% of the site index)
2. We track index sizes of each of our subfolders, especially to see the increases in index sizes of our daily-published content, and also because GOOG's "site:" search with a date qualifier usually returns wrong results
1. Why would the index go up so much so suddenly? From where can it get so many pages suddenly?
2. Could the (slightly abnormal) traffic increase in the week after the index size increase and its subsequent reduction be a result of this index fluctuation?
Thanks for your time