Expected dates of Next Google PageRank Update for year 2012 are:
Google January PageRank 2012 Update
Expected time: 30 Jan, 2012 – 2 Feb, 2012
Google June PageRank 2012 Update
Expected time: 30 Jun – 2 July, 2012
Google October PageRank 2012 Update
Expected time: 30 Sep – 2 Oct, 2012
Google December PageRank 2012 Update
Expected time: 31 Dec – 3 Jan 2012
More info on : seo-trafic.eu/next-google-pr-update