I agree - it's extremely painful and extremely mysterious why some sites (and I'm sure it is in the thousands) have been nailed by Panda. There are many pandalyzed sites I've seen that don't seem to show the kind of low quality signs that Google has described as being Panda's target.
Now that we have another confirmed Panda iteration, I hope more revealing data can be accumulated by SEOs so we can dig out of this mystery - and it is definitely a mystery to me and many others. There are sites that didn't get demoted and still seem to be in the various profiles that many assume is at work.
We don't see Panda clearly - and that's about all I have to share right now. The easy answers just don't work.