To be honest, I find it hard to believe that there haven't been any changes to the algorithm or some kind of mass flagging or something. From November 5th to 8th we've lost 70% of our traffic, and I've seen complaints from many developers about the same period.
And ever since we continue to drop in the Popular lists for tags. Around Nov 5th, we were on the fourth row in Popular for our main tag, and today we're in 3000th place in Popular for the same tag, even though the traffic to the page has stabilized.
I understand that the algorithm needs to be opaque to prevent exploitation, but it would be nice to at least know the big no-no's that could cause this kind of fall.