Now that we know that toolbar PageRank does not mean all that much, in terms of ones ranking at this point in time - we can discuss a possible bug in the Google Toolbar.
A WebmasterWorld thread has dozens of people reporting that old and trusted sites are now showing a PageRank 0 (PR0) score.
If it happened to their site, some are clarifying that they have seen no significant change in traffic data. That is just one more sign that the toolbar PageRank doesn't impact your rankings directly.
But is there some sort of bug with the toolbar?
Forum discussion at WebmasterWorld.
