AlyssaS - 1:39 am on Dec 24, 2011 (gmt 0)
Whitey - it's not a Panda update. That's actually helpful because it means it's something else! All year G has been slipping other updates in at the same time as Panda and people have been befuddled. At least this time you have clarity.
From other forums, some people are reporting sites are responding to new links, which means the problem must have been link based. So check out your backlinks, are they still indexed, are they still there? (I've been unaffected, so am just throwing out suggestions here).
P.S. I'm pretty sure the previous update (Dec 13th) was to do with duplicate content because my competitor, dropped to page 2 for the first time in months (they had nabbed him in the original duplicate algo back in Feb, but then loosened the criteria and let him back in - part of his content is duplicate, I now need to sit down and work out percentages so I know what amount seems to trigger the drop)