PageRank Update July 2011
After many months of no change Google decides to update toolbar PageRank twice in a row. First in June  and then in July. After a bit of investigation we found a post on Search Engine Round Table  which seems to clarify the issue. Apparently the whole July update rotates around glitch in PageRank calculation of Twitter (which was given a zero in June). Many webmasters speculated this may have been the end result of changes in Google and Twitter business deal, others suspected Google may have penalised Twitter for some reason. Neither was true and in the letter to Barry Schwartz Google writes:
“Recently Twitter has been making various changes to its robots.txt file and HTTP status codes. These changes temporarily resulted in unusual url canonicalization for Twitter by our algorithms. The canonical urls have started to settle down, and we’ve pushed a refresh of the toolbar PageRank data that reflects that. Twitter continues to have high PageRank in Google’s index, and this variation was not a penalty.”
It is unclear at this point whether the recalculation of the PageRank took place outside of link graph directly affected by Twitter but this domain was obviously too big to ignore in the overall scheme of things.
Our SEOs confirm that PageRank re-calculation did not gain any depth and the dates taken from May update remain the dates for July update (9th May) only with corrected values after Twitter PageRank fix. What is interesting is how quickly the new calculations happened and is likely due to their recent framework upgrades .
Another toolbar PageRank regular update is not expected any time soon.
 PageRank Update June 2011:
 Google’s Latest PageRank Update Breaks, Google.com Back To PR 10:
 Relationships in Large-Scale Graph Computing: