Google PageRank Update Schedule for the year 2011:
First 2011 PageRank (PR) Update
Time-frame: 31 January - 3 February
Second 2011 PageRank (PR) Update
Time-frame: 30 June - 3 July 2011
Third 2011 PageRank (PR) Update
Time-frame: 30 September - 3 October 2011
Fourth 2011 PageRank (PR) Update
Time-frame: 31 December - 3 January 2012
All these updates are major PR updates.
The data is the assumption based on previous PR updates.
Google Generally updates website or blog PageRank PR 4 times in a year.
Third 2010 PageRank (PR) Update
Time-frame: 31 September – 3 October 2010
I think the 3rd PR update takes place in the end of October :) Let's wait and see.