tedster - 3:32 am on Dec 8, 2012 (gmt 0)
the hit was 29th Nov. Now marked on my stats chart as possible unannounced Pands update.
There was a confirmed Panda Update on November 21 - see [webmasterworld.com...]
It's very unlikely that another happened 8 days later. It does sound from the observations here like some kind of algo shift was going on Nov 29, but I'd be very surprised if it was Panda.