The one thing that helps some web to attain PR4 is the backlinks from
http://wordpress.com/tag/….
In order to get these backlinks, you will need to categorize each of your posts. You will need to categorize your post according to the WordPress.com tags.
For example, I will put this post under the category of pagerank. When I do this, my blog post will be added to wordpress.com/tag/pagerank which is a PR5 web page. So I will get a PR5 backlink to this post.
And I will also put this post in the category of blogging. The page, wordpress.com/tag/blogging is PR7 and this new post very likely will be spidered by Googlebot within hours.
So, this post will get 2 backlinks with PR5 and PR7. It’s easy, isn’t it?