I thought there was a consensus a few years back that -900 (end of results) penalties are the result of duplication, either inter- or intrasite, perhaps with some unintended queries as part of the URL or canonical issues. Has this thinking been completely supplanted by concerns of over-optimization. I just got myself a site which, while I was down without power, thanks to Sandy, got hit with -900 (number fluctuates, so "end of results" is a better name).
I've never really done any optimization there, so it would be hard to see how it is over-optimized but I do see mysterious 190,000+ "blocked URLs" in WMT. I don't know yet what they are (just got the power back a couple of hours ago) but they seem like something URL parameters may create.
So, do you think it makes sense to still pursue the old dupes theory?