Last time there was a big Penguin update by Google, i.e. Penguin 3.0, Google did not announce that it happened but they confirmed it after we asked about it.
Google's John Mueller implied they would do the same thing next time a Penguin algorithm is updated or refreshed.
He said in a Google+ hangout at 1:17 in to the video when someone asked about Google announcing the next Penguin update. John said:
I don’t think we'd pre-announce it but if this is something bigger that happens that people have been waiting for we will try to confirm it.
According to my records, there has not been a Penguin update since early December and it is unclear when the next one will happen. So we know Penguin is not running monthly or regularly yet but it is a goal they set out with. Although, at one point Panda was and maybe it stopped?
But when it does, I am sure we will report it quickly and get Google to confirm it.
Forum discussion at Google+.
