The whole world is well attentive of the fact that Google updates the PR for websites and blogs 4 times a year, but no one has clear idea when it happens, assumption about precise date can be made and sometimes it ties with Google.
Google changes its last PR in the 30 Jan, 2012 – 2 Feb, 2012 that was an awful update for most of the webmasters and bloggers, as Google has strengthen the circle against spammers and copyscape. This update might be more abrupt then the previous one as now Google is changing its algorithms on daily basis after a major Penguin Update
