First off, if you don't know what Google PageRank is, then here's a quick
introduction to Google PageRank
Most SEO experts are of the opinion that the Google PageRank number that is available to the public (often known as the "toolbar PageRank") is not very important. The toolbar PR (TBPR) is the number shown via the Google Toolbar and other software applications (like WebsiteGrader.com's SEO Report . SEO experts think Google PageRank is not a particularly meaningful number for a variety of reasons:
1. Updates happen infrequently (every few months)
2. Updates happen inconsistently (you never really know when the next one is coming)
3. It's a coarse number (0-10 -- no fractions) in comparison to the "internal" PageRank number Google uses for its ranking algorithm.
All of these are legitimate reasons that do indeed severely limit the utility of the public Google PageRank. However, this number continues to be interesting to many folks primarily because it is the simplest abstraction that can easily be accessed to determine the general "authority" for a given web page. It factors in the two most important things from an SEO perspective: The number of inbound links to a given web page and the power/authority of those links.
So, although Google PageRank has its limitations, it continues to be monitored and cited (if you're in the market for buying a website, one of the things you'll likely look at is the Google PageRank of the site).
Now that we have that out of the way, let's talk about the update cycle. The last known update to the public Google PageRank number (as shown via the toolbar and tools like WebsiteGrader.com), was around April 30th 2007. So, as I write this article, it has been over 4 months since the last update. In all the time that I've been watching the Google PageRank updates, this is the longest lapse I've seen. This likely means that we're going to see an update "any day now".
What does this mean to you? If you have a relatively new site, or have just started getting meaningful inbound links recently, don't fret if your Google PageRank is zero. Since there hasn't been an update in a while, chances are your current PR (or lack thereof) is simply based on the old data. Once the update occurs, you should see yourself move up. WebsiteGrader.com is currently at a PR5 (which is not bad), but I expect the site to jump to a PR6 as it has more powerful links than some of our other sites which already have a PR6.
If you're interested in knowing when the next Google PageRank update happens, I have a simple solution for you. Just register for this site and we'll send you a quick email when the update happens. We monitor hundreds of websites on behalf of our users, so when the change happens, we'll likely be one of the first ones to know -- and so will you.