1script - 3:09 am on Nov 19, 2012 (gmt 0)
Not to give you a bigger headache than you already have but I just went from about a month of mismatched traffic to 50% less traffic overnight. My hunch is that mismatch leads to lower UX values which gets fed back into the ranking algo and that becomes a positive feedback loop.
Funny thing tho: about two days before the traffic dried up, they threw nice converting traffic at me. Lasted for about 36-40 hours, then half of it is gone, zombies as well as "normal" people that were coming in those nice 36 hours. And, BTW, what's still coming from Google can be described as "slightly warmed up zombies". Better than it was before, not even close to same season last year.
Don't have much analysis done yet- the trouble is very fresh, I'll need a few days to look at the data (and WMT will catch up with search terms data, too) to see which KWs did I lose. It feels like I've lost the "shorter end" of the long tail but it's hard to tell for sure yet.