whatson - 4:06 am on May 24, 2011 (gmt 0)
I think it is best to think of Panda like Pagerank. Every now and then they will update your Pagerank by analyzing what links you have. Well I believe every now and then they will update your Panda score by analyzing what quality of content you are offering.
It could just be the same update as when they update their index, which has not happened since Panda anyway.