Shaddows - 4:10 pm on Nov 2, 2012 (gmt 0)
We also enjoy long periods of stable referral patterns. We find that a significant referral shift is followed a week or so later by a general re-ranking for our site, which is not part of a main algo update.
The reason for this seems to be a re-profiling of the site- at the whole site level. In the past, we have seen completely different customer behaviours either side of a shift. Having been through the process on many occassions (and always one in late Sept to early October), we have contingencies to cater for most valid user-intents, but it usually turns out for the better, eventually.