Looks like Google is increase the frequency of the nominal Pagerank updates. The last one happened exactly two months ago, there are rumors that the new one is taking place this weekend.
The clue is coming again from Mr. Matt Cutts. He stated the following on a comment on his blog two days ago:
I wouldn’t be surprised if new PageRanks started showing up this weekend or so.
Personally I find it weird to release a second PR update two months after the latest one. If you remember well, last year we passed almost 6 months without seeing one. Perhaps Google is tweaking their algorithm, so they need to update things more frequently?