Middle of last week, Google pushed out an update to Panda, the Panda 2.5 update.
DaniWeb, one of the loudest and most vocal sites hit by Panda early on, which recovered, got hit by Panda 2.5. So she got vocal again and yesterday they recovered. Dani said in all caps yesterday afternoon, "WE HAVE JUST RECOVERED."
She later on explained, "No, today is our busiest time of the year. Traffic literally went down by 50% on Wednesday and went back up by 50% today."
Danny Sullivan has been pressuring Google behind the scenes to give us more on what is going on with Panda. I think, not certain, it lead to Google's Matt Cutts to tweet a "weather report" (Yahoo first named search updates weather reports back in the day), on Panda:
So, I am not sure if DaniWeb was the first tweak to Panda 2.5 or if it was something else. But do expect more tweaks in the upcoming weeks.