not sure.. but i think its a part of their update.. just like what they said about PageRank: "We have always taken a pragmatic approach to help improve search quality and create useful products, and our technology"
I like fast, monthly PR updates. I don't think its much to worry about though, just concentrate on getting more links with good anchor text to your homepage (and subpages).
It is unclear if Google's toolbar update have changed frequency or if the last few months have been an anomally. My advice focus on ranking well, forget the toolbar ;-)
PR is totally a useless thing and takes away lot of focus and attention of webmasters without any incremental benefit except may be selling a link or two from their site. Increasing the frequency of such updates will make people, even more crazier than ever before! Regards, RightMan
To what i have read, Google updates PR every 3 months. In 2009, the PR was first updated in March(i think) and now it was updated in June. Still its a 3 month gap for PR update. Expect another update of PR in Sept. 09