After its update of Page Rank on Feb 4 2013, Google has yet another update. This update of Google for it's Pagerank will be somewhere in the month of May. We can verify this from the info given below.
The previous update of Pagerank was on Feb 4 and the other one, i.e before Feb 4, it was updated on November 8. Now rectifying both these dates, we can notice that there is a gap of almost-three months. Here's the proof that the previous update was on November 8, click here. (that of Feb 4, I guess I read it somewhere). Within these three months, the gap between Page Rank's update, we can make a good and un-spammy blacklinks to our blog either by commenting or by contributing a guest post with your blog's url along in a highly ranked site that are accepting the guest posts.

You might also like: What is PageRank all about?

Everyone, the bloggers and other website holders are always eager to know the way to get high pagerank for their sites/blogs, the easy way to get them is by getting a good reputation to your site. 'Reputation' here means, as per Alexa, is the number of websites where your blog is linked to. Here's an real life example, when people are always talking about a Famous Person his reputability increases. If one says that he's good or something more than that, then the other people show their opinion. If these opinions are good, he becomes famous around and then known to most of the people. Similarly, if a blog has got reputability, by mentioning them in other's blogs/site which has got Good Page Rank, then Google also thinks that the site(linked in others) is also equivalent to them and also gives an equal rankings.
(Why comments with dofollow and guest posts were started?)
This can done only by the admin by mentioning about your site. But, some geeks, in order to get good comments and pageviews to their site and form a "relation" with the readers, discovered a way to accept comments, so that each and every users can get a backlink to their site indirectly and thus advantages for both the admin and readers.

Get some cool backlinks to your site from PR 9 and PR 8(five each) sites just by commenting. CLICK HERE.

Apart from this, geniuses also paved a way to get more post at their blog just by giving two or three backlinks to their site of the writer.

So here you read about the way doffollw and guest posts were started. But the date when the PR is going to be updated, after its February 4, 2013 update, is not known exactly. Google doesn't share about! The conclusion of the date is quite difficult, but for sure it'll be somewhere in May.