The more I look into this, I see two ingredients that are common to all of my sites that got hit the worst. Bear in mind that these are adult sites with good hand-written content, so "content issues" either on the money site or on web 2.0's (which don't exist because they're adult sites) aren't in play here. 1. Biggest commonality: They all had XR blasts directly to them within the past year, mostly about 9 months ago. (They're all very aged sites, so I considered them "safe." 2. Second biggest: lack of anchor text diversity. But a few sites that were "XR-free" but still don't have a lot of anchor text diversity did OK. Conclusion (and it's still early): backlink profiles are definitely a part of Penguin. There are no content issues that could be at play on these sites. My big question is: is this a timed penalty that will expire (meaning that waiting and link building would be the correct approach), or is it a death penalty (meaning either 301s or abandoning sites)?