Lorel - 6:03 pm on Feb 26, 2013 (gmt 0)
I experienced a slow drop on Jan 31 and eventually lost about 1/2 my traffic (which is about 1/2 of what it was 2 years ago) and it's still slowly dropping.
There was a similar drop Starting Dec 2 then traffic slid for a month until Dec 29 but that didn't affect main keywords so I assumed it was due to the holidays (I don't sell products - only services).
Then traffic picked up again until Jan 31 (reaching the previous high peak) when it started dropping again slowly but this time it has affected main keywords. I had already deoptimized all those pages months ago but I just did it again and updating pages I haven't touched in a couple years also. I have several pages that still rank highly and bring a lot of traffic but not income generating pages.
This isn't the first rollercoaster ride this site has experienced in the last 2 years although it has been better than last year. I am assuming it's because I hadn't updated enough pages last time.
I don't see a panda update around Jan 31. Have you seen one?
BTW, I have had some success fixing pages where the title and H1 tag were using the same keywords and also repeated in first paragraph.