I have a site that has exhibited a few up and downs (mostly downs though) in the last couple years - started few months before and continued pretty much all through the Panda age (early 2011-current). However, one thing that stands out for me looking at the traffic stats - neither the ups nor the downs have ever coincided with any of Panda refreshes. The exact dates of Panda refreshes and several days before and after always look very unremarkable for this site.
The site has lost approx 70% of its pre-2011 traffic and yet Panda has never touched it (or so it seems unless it bites in-between refreshes, too). So, what can I infer from that data - the site's quality is good (if Panda was ONLY about quality, however it's defined) yet some other parameter is bringing it down? What would you infer from Panda refreshes having no direct effect on traffic to a site and yet the overall trajectory is downward?