A friend pointed out a scenario that could be coincidental or not, so let's discuss. DMOZ, as you all know, has been having its share of problems for a while now. At times, hitting the site causes it to be redirected to a subdomain of aol.com (and other times not). On some datacenters, there are far fewer pages listed in a site: command for DMOZ than on others. Now, just thinking out loud here…
Suppose Googlebot hit those redirects to aol.com enough times
And suppose those redirects mangled the previous www to non-www redirect that DMOZ had in place, so that on many pages, the version with PR (non-www) isn't cached, but a PR0 version with the www is cached.
So, in an amazing combination of flawed technical know-how, the 2 web superpowers, AOL and Google, managed to destroy the authority of an old "authority site" (which expires in a couple of weeks, btw). AOL, by not knowing how to do a proper redirect, and Google, by not knowing how to deal with it.
(Examples at the time of this post: PR5, uncached, http://dmoz.org/Arts/Literature/Poetry/ and PR0, cached, http://www.dmoz.org/Arts/Literature/Poetry/)
Now suppose many of the DMOZ pages got deindexed due to this blunder and the links on those pages were no longer counting.
And suppose a trickle down effect began to happen with loss of PageRank / link value for those links to those sites, and the sites that link to them that have lost links, and on and on?
Now, let's suppose you've lost some rankings and don't know why. Yet, you still have your rankings on one or two datacenters. Now suppose, a site: command for DMOZ on those datacenters show a lot more results than a site: command for DMOZ shows on the datacenters where you've lost rankings.
Coincidence? Maybe. But what if…? Any thoughts?