I suddenly see a change in my highest PR page as reported by Google Webmaster Tools. It used to be the homepage, obviously, until October 2006. One both months - October and November the pages shown as highest PR are what seems to be just random internal pages. The homepage is PR4 (down from long time PR5) and the October page is only PR1 and November page does not even have any PR at all according to the Toolbar.
I've heard a few similar reports - and in those cases, there was no related change to traffic or rankings. I'd guess some reporting-only bug has slipped in, or perhaps G is still tweaking their toolbar PR report and some more jiggling is in store. I any case, unless traffic suffers I would release worry for the moment.