I have seen numerous reports recently of sites seeing their Google PageRank dropping significantly, then a few days later returning to where it was. This happened with Google's own .com website - it dropped to PR9 for a week or so and then bounced back to PR10. Twitter dropped all the way down to PR0 before returning to PR9. It is now widely known that Google only update toolbar PageRank roughly every quarter, so this double update that has been happening indicates there has been some issue. Unfortunately there has been no further explanation from Google. It also raises the…