We had two PageRank updates in June of this year already. However, this latest Toolbar PageRank update seems to be relatively minor and impacts only a small percentage of web sites out there.
Starting on June 20th or June 21st, some people began reporting seeing their PageRank change in the Google Toolbar.
We have threads at DigitalPoint Forums and several at Google Webmaster Help.
This is minor, most people were not impacted. It may be one of those PageRank penalty cycles where sites are hit for buying or selling links. But again, it is a minor update and not noticed by most.
Forum discussion at DigitalPoint Forums and Google Webmaster Help.