Planet13 - 7:13 am on Feb 13, 2012 (gmt 0)
What would you do if it was your site?
Check, double check, and then TRIPLE check for any possible structural errors.
Do you have an XML sitemap? Is it pointing to the correct URLs? Is your robots.txt file correct? Is it possible that one or more of your significant pages has a noindex tag on it?
Also, if the blog is as distasteful as you say it is, why keep it around? Does it generate much revenue for you?
I don't have any direct experience with Panda fever, but it seems like it is a bug you are likely to catch eventually if you have a lot of "regurgitated" material.