Panthro - 3:44 pm on Mar 15, 2013 (gmt 0)
we noticed the traffic drops one week before the official announcement. So we actually saw the drops around the 7th, same as previous Panda runs we saw drops 7 days before the official date.
That seems pretty characteristic of all these Panda updates, with a big spike in visits the day before (Lots of visits across the board on my sites March 6th). I wonder if this will continue to be noticeable as it becomes less of a big, separate update.