This is a new Panda algorithm, not a refresh that we've seen almost monthly but enough for Google to name this 4.0, which means a new algorithm update to it.
Google's Matt Cutts told us at Search Engine Land that this Panda 4.0 update impacts ~7.5% of English queries to a degree that a regular user might notice.
Also when I spoke to Matt Cutts, he made it sound like this update may appear gentler for some sites but it does lay the groundwork to future changes in the direction of a softer and gentler Panda algorithm.
This began rolling out yesterday and is unrelated to the Google Spam Algorithm 2.0released over the weekend and unrelated to anything Penguin.
So no, I was not crazy expecting something big that happened over the weekend and throughout the month and this week. Even though Google said nothing is going on, we've been seeing signs of major changes and ranking shifts all throughout the month. I suspect those were tests for both this Google Spam Algorithm version 2.0 and the Panda 4.0 release.