Google tweeted today that it launched a data refresh for the Panda update on Monday. According to the company, about 1% of queries were noticeably affected.
Panda data refresh this past Monday. ~1% of queries noticeably affected. More context: http://t.co/nSjVRWGb
This is the first known Panda-related tweak we've seen from Google in August. In June, Google incorporated new data into the algorithm, and launched two data refreshes. In July, Panda was launched on google.co.jp and google.co.kr Additionally, Panda data was updated again.
Keep in mind that this latest adjustment was just a data refresh. These tend to have a much smaller impact on results than actual updates. For more on the difference between an update and a data refresh, refer to what Google's Matt Cutts has said on the matter.