Sand - 2:30 pm on Mar 13, 2013 (gmt 0)
Nobody knows, gford. But it's possible, yes -- from what I've seen here, that does happen sometimes before a Panda update.
But at the same time, I've seen a smallish (10%) drop in traffic for a week or so before making gains through a Panda update. There's just a lot of overall fluctuation while they're testing (I assume that's what happening, anyway).