Over the weekend, I have seen tons and tons of threads in several forums with webmasters and SEOs complaining that their PageRank score in the Google Toolbar took a dive.
The thing is, I didn't see anyone happy with the new PageRank score they received. If you look closely at the Google Webmaster Help you will see, Googler, JohnMu say:
Looking at your site, it might have been that there was some kind of glitch that occurred just as the latest round of Toolbar PageRank was put together. In a case like that, you just need to wait for the next update (we do 3-4 updates per year). That said, this is generally not something that will affect your site's crawling, indexing or ranking, so I wouldn't worry about it! Don't worry about PageRank :-).
So, with this guys particular site, there was an issue exporting his site's PageRank to the Toolbar, during Google's quarterly export. There may have been other issues with other pages impacted by this export.
I don't know for sure, but what I do know is that we should not worry about Toolbar PageRank.