Matt just posted that the latest Google PageRank update is now underway as well as updates for the link: and site: commands. PR values are fluctuating wildly during this time, but as with previous updates, should settle down in the next 48hrs.
He also reiterated about how Google is treating certain types of links and that the lack of link quality could be causing some pages to go into supplemental.
“If you used to have pages in our main web index and now they’re in the supplemental results, a good hypothesis is that we might not be counting links to your pages with the same weight as we have in the past.”
The major determining factor of a page going into supplemental is its PageRank value. So if some pages are identified as being a bit spammy, they aren’t assigned any (or maybe only a tiny bit of) PageRank. This means that the PR calculation has a new dynamic element to it, which may be part of the dampening value in what we know as the standard PR formula.