Monday I reported some weaker signs of a Google update but things settled down a bit but is now spiking higher this morning.
A senior member at WebmasterWorld wrote today:
I'm seeing quite dramatic changes in SERPs today, I suspect quite a major update of some sort is crunching... too early to tell if it's Panda.
Some suspect EMD, some think Panda, but it is hard to tell if it is anything at this point.
Forum discussion at WebmasterWorld.
Update - No Update: Google has informed me that there was no update. Here is their comment:
It's not Panda. We asked around a little bit and didn't uncover any other likely suspects, but remember that Google launches over 500 algorithmic changes per year, so there are always small changes rolling out.
Update #2: Google a few days later announced a Panda refresh:
New Panda data refresh rolling out today: 1.2% of English queries affected. Background: goo.gl/8Zqy1— A Googler (@google) January 22, 2013