Here we go.
Over the past year, we've seen countless forum posts of people talking about getting hit by various iterations of the Panda update. Sometimes it really was Panda. Sometimes it wasn't. Google, of course, makes algorithmic changes every day (over 500 a year).
Now, we can probably anticipate a similar trend with webmasters thinking they've been hit by Penguin. Again, sometimes this will probably, in fact, be the case. Other times, it may not be.
Some are currently talking like there may have been a Penguin update within the last couple of days. Barry Schwartz at Search Engine Roundtable points to some discussion in various forums, and speculates that it may have been Penguin (he's already got the "1.1" name for it), though so far, this has been unconfirmed.
While many of us assumed Penguin would operate in similar fashion to Panda, in that it would come back every so often, Danny Sullivan at Search Engine Land confirmed this to be the case with Google's Matt Cutts last week. This means we'll continue to see more sites get hit, and probably some recover as time goes on.
We've reached out to Google for confirmation of whether this was a Penguin update or not. We'll update accordingly.
For stories about Penguin and various tips (many either straight from Google, or endorsed by Google in some way), please peruse our coverage here.
Update: Schwartz now says Google has confirmed that it wasn't a Penguin update (or a Panda update, for that matter).
500 changes a year.