Turns out the Penguin update isn’t fully adjusted, according to Google’s Matt Cutts, and that websites can expect several “jolts” in the upcoming months as Google continues to refine the algorithm. As far as the Panda goes, the update is focused on low-quality pages, and is minor enough that we should hardly notice it. Panda will continue to be updated on a monthly basis in this manner.
The reason that Penguin updates will carry more weight are because the algorithm is still new, thus the adjustments are going to be bigger, but it will eventually smooth out over time just like the Panda update has. The Penguin update algorithm was created to penalize sites that spam Google, though they claim it isn’t a penalty but more of an adjustment that doesn’t reward spam. One of its main functions has been to discredit linking activity that wasn’t up to Google’s standards.
Since its April debut, Penguin has only gone through one update in May. It was a relatively minor update that affected less than 0.1% of all search results. The dates of any future updates were not revealed, but given that it’s been three months since the last update, the next will probably be fairly major.