Pagerank is mainly depend on backlinks but ranking depends on backlinks, content, header tags and many other factors. Check the content for duplicate as your site ranking affected after panda effect. So, to improve the ranking do the competitor analysis and make changes in your site if necessary.
All your legit hardwork has paid off. I can name a few guys who have suffered at the hands of this panda. But you are among the lucky ones and you have been given the fruit of your work.
It also happened to my humble site. we're currently facing some problems right now regarding the update. I wish that it will comeback to normal. The Google update is always unexpected and this it pull us down. BTW: I wonder when will be the next update is. It really is sad to be pulled down.