G. PR updated gave me lot of trouble. One of my site was in PR 6 which is now in PR3. Its really pathetic.
No, its not changes but Firefox changes and update there latest update so that our plugins are not updated that's why its shows PR zero for every page.
Nice that they finally updated, but Google has always stressed not to worry too much about a PR update but to focus on getting quality backlinks and unique content
Google analyse the link popularity and assign PR as you know...PR update usually after 1 and half month as I notice