It appears that Google has revised the PR value that displays in its toolbar. This is because all of my PR5 sites are now displaying as PR4.

My PR6 sites are now showing as PR5.

Google has been doing this for quite some time. They have to. Everyday, thousands of more websites make their way online. Hundreds of thousands new links are added. Considering the fact that the toolbar categorizes each site into one of eleven rankings (0-10), they have to recalibrate the rankings.

This doesn't mean our websites have lost ranking. Rather, it means that a PR5 rank now has the influence of what a PR6 had.

The ranking on the toolbar is not the same as the "true" ranking. Google assigns a very large number, several digits in length, as your real rank value. What appears in the toolbar is simply an abbreviation of that number.

So, your ranking hasn't really changed.