It's going to depend on the type of site. And whatever metrics Google is using, I'll bet they are also customized by type of site. That's the kind of thing they've been doing for a lot of years.
The best answer I could give mis this. IF your site was hurt by Panda, start the way claaarky did. Collect the data for your site and see if there's a correlation for you. If you see a correlation, then dig in. If you don't see one, then move on to another approach. Otherwise you just might break things even further.
The key for me is taking that "open eyed" look at "your own baby" and being willing to notice when it's ugly instead of beautiful. It's not in some automated data/technology approach, it's in the human intelligence. The data just helps you focus.