Google is never going to lay out exactly what each update covers, but they typically touch on it a bit. I have found the Inside Search blog by Google to have some decent information. Otherwise, Google Panda 3.3 and 3.4 for info on the 2 most recent updates.

There are lot of changes in the google panda.

If you have more ads in the website like kontera, Adsense, text links your site is going to be

low valueble site with respect to search engine( google) .

And lack of quality content in your website is also a another chance to get low value.

So always you need to maintain the website with good quality content .

When google panda udated , lots of website lost there ranks because of panda

recalculated every month and collects the user statistics and quality of the

website.

Changes that we have seen are:

The New Play Tab
The Google +1 button.
Google Panda Update.

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I'm really pleased with the new update, all my sites have climbed the SERPs, and one has jumped from page 10 to page 2... don't know what exactly changed to cause that increase, but I ain't complaining.