My recent Panda experience:
I have a site that soared through all the Panda iterations of 2011 and early 2012. This is a site that I never touch. It is established, with some useful tools and under 40 pages of content. Then, in February, I thought I would "freshen" the site up by adding two new articles that I had written over the past few months. A few weeks after adding those articles (most recent Panda iteration of March 23), I was hit by a 35% to 40% traffic reduction. My first reaction (perhaps not the best course of action) was to undo all changes from the preceding 30 days. I removed the articles and returned 410. Again, since this site is never touched, I feel like the new articles may have tipped the scales. I had also bolded my primary key phrase at least once in each article (i.e., very minor on-page optimization) which may have rendered them "shallow" or "overly SEO'd" when compared to the rest of the site. Nevertheless, they are gone now and the site is now as it was in mid February. Maybe rankings will recover in the coming months. I've always had luck in undoing changes leading up to a ranking reduction. The alternative is to wait it out, but I don't think that will do any good.
Long story short, my BEST-performing sites with respect to Panda are those that I never touch. Old sites that are never tweaked/changed have fared well. There have been a lot of Google algorithm changes in the past month, so it's hard to know with certainty what lead to the traffic reduction, but it correlates well with the date (March 23) of Panda 3.4.