caveman - 4:56 am on Jun 7, 2007 (gmt 0)

This all seems to point to a new algo modification.

Agree. Usually I reach a working therory within a day or three, even if it turns out to be wrong; at least something to investigate that might explain what is going on.

But this combination of weird geo components and high quality, authoritative sites dropping off on core searches has thinking that mulitple signficant alterations are happening simultaneously.

My best theory so far -- Two changes: Geo-related, plus some sort of relevance shift...probably related to a bad semantics assessment. At first I thought the relevance issue was age-related, but both newer and older sites are suffering in some respects, and only on some kw's. So I'm now looking at SERP's where good rankings fell away for sites that should still be ranking, AND where those sites still rank well some but fewer important terms.

A category that relates to my area of professional knowledge is of particular interest, but it't not hard to find areas to investigate.

For any of the wiseacres out there, it has nothing to do with P-P-C ;-)