tedster - 1:52 am on Mar 24, 2012 (gmt 0)

So it must be some update they've rolled out, if not Panda then something equally significant.

I agree - there has been some other major update rolling out this week, but it was before today's Panda iteration. Others in our March SERP Changes thread [webmasterworld.com] have been reporting the some kind of thing.