ecomconv - 1:08 am on Sep 28, 2011 (gmt 0)
I know it's been a while but this is a really interesting thread. The nature of your traffic obviously changed related to Google Panda's release. I think the easy response here is to look at the top keywords in traffic sources you had before and after panda. That should show you that you had more qualified relevant visitors before.
There might also be a change in the effect it had on your PPC campaigns.