A thread over at WebmasterWorld has some reports of a PageRank (PR) update going on with many people seeing new PR values, just one month after Google did their last PR update.
It will be interesting to see how this plays out during the course of the day... is this an incremental update or a full PR update? Are Google returning to their monthly PR update cycle from many years ago? It's not impossible... as more new content is generated, people want to see the PR values for those pages. Leaving PR updates on cycles of just 6 months leaves huge gaps in the number of pages for which Google has missing PR values. That can reflect poorly on Google.