I changed my site be cause I was hit in april 2011 by Panda, slowly changed the site, done 2 Month ago, but no change in ranking, my stats is like this
1. Bounce rate down from 82% to 46%
2. Visitor time on site down from 0.45 to 1.55
3. Spam increase and Zombie Traffic : i dont know
4. Returning Visitors down by : I think the same as before
I will not say my site is better be cause of the bounce rate, be cause before they got directly to what they want now that last page has gone, so they get to a page with more options. The cms, design, text... all changed title somewhat the same.
I think Panda just dont work as a ranking factor, the serps are simply pure and in my example, how can a site with 60.000 visits a day suddenly be crap, its no affiliate site or article site.