It's worth remembering that nothing is truly static at Google - the tweaks are onging all the time - and that as things creep or roll along, as the case may be, there are changes which are often more-or-less temporary.
It's also worth remembering that
PR does not equal ranking in the search engine results. In this latest tweak, my
PR dropped slightly, as did another site I'm associated with professionally. However, my two main competitors also saw
PR drops, greater than either of my sites, and so in the end my search engine placements are either the same or slightly improved for my 4 major search phrases.