tedster - 8:47 pm on Feb 27, 2008 (gmt 0)

PR "updates" are not a sign that your PR just changed for a given url. They are PR "exports" to the toolbar, derived from the PR values that Google is already using to calculate the rankings. PR "updates" never have an effect on traffic, because you would already be SEEING the effect, long before the export.

When a new export occurs, that is the most recent data you can see, and it may only be a couple weeks old. And then it continues to age until the next update - usually in about 3 more months.

The present time value for PR is continually updated privately by Google and folded into your ranking calculations all along. But the toolbar report shows this historical snapshot that begins at a few weeks old when first exported, and then ages for however many months go by until the next export.