After June 2009, Google Page Rank next update was definitely expected in September 2009, but now there are some news coming as Google has started the process and the changes may reflect in end of October 2009. Google updates the PR at an interval of 3 months or so but this time they are taking more time. Google just released the Google Wave and then they are also busy in Google Caffeine. Webmaster team is also busy in the upgrading the Webmaster Tool. But this time lot many websites confirming the news that Google has started the process and they will be done by the update by end of October 2009.
Also Read: How Google Search Engine Works! Explained In Simple English
Here are some excerpts from other websites about the Google PR Update,
For those interested in rakings, backlinks and Page Rank, Google today has started the PR update and backlinks update. – Marketingeasy
From many sources, including google themselves, the next PR update should be in this month, October 2009. So be prepared to a Google PR update by the end of this month. – Web Code
Be prepared to see the update on Google PR of your website or blog in this month or at most by first week of November.