I cannot tell you how many times we see threads that are either reporting or questioning if there is a Google PageRank update. We try to document all "real" toolbar PageRank updates here, but often, very often, there are smaller updates or not updates at all, of the PageRank bar, reported in the forums.
I figured I highlight one such thread, because Google's JohnMu adds some insight into why people might see a PageRank 0 or update before its time.
A Google Groups thread has one member worried that his PageRank dropped from a 4 to a 0. John, from Google came in to ease this webmaster's concern. He said:
Keeping in mind that we only update PageRank for the Toolbar a few times a year, it might be that there was just some "fluke" with regards to your site right when we updated it. For example, it could be that at that moment, the www- or non-www version was more relevant, now that other version is. At any rate, I don't think you need to worry too much about that :). Two things that you could do are setting a preferred domain name in Webmaster Tools if you haven't done so already and setting up a canonical redirect to that preferred version.
- Toolbar PageRank is updated every few months
- Other updates are likely flukes due to canonical issues or issues contacting Google's servers.
Forum discussion at Google Groups.