As most people in the SEO world know, the Panda update algorithm is used to weed out low-quality websites from the top ranking spots in the search results. Over the years, Google and it's users have had to deal quite a bit with websites that produced low-quality or even copied content. With Panda, Google has been attempting to learn to identify low quality websites and provide users with higher quality sites when they do searches.
Google recently let us in on the Panda update cycle of which they called a "rolling update". The rolling update occurs approximately once every month or so, but yesterday's update is considered to be more substantial. With yesterday's update we can safely assume that more people will see the effects on Panda in the search results.
With that said, we are also expecting to see many webmasters and SEOs posting their distress online. When Google makes major updates to their ranking algorithm, there's no shortage of outcries from webmasters and SEOs but despite these outcries, Google is quite aware that these updates actually contribute to a better user experience for their users.
According to Barry Schwartz of SearchEngineLand.com:
From talking to Google, it sounds like this update will be gentler for some sites, and lay the groundwork for future changes in that direction. (source)
Please note that at the link above, you can also find all the dates of previous Panda updates.
Should website owners and SEOs be worried today? The one way to be sure is to determine if your website falls under Google's quality guidelines. By continuing to put your website through quality checks, you can, for the most part ensure your website is standing up to Google's guidelines and providing users with a decent experience while they are on your website.