Dofollow blogs is where bloggers gives dofollow link to commentators, which has no rel=”nofollow” tag added on commentator’s link. It is one of the popular types of link building, but only small number of blogs participates in dofollow movement. As for this blog, I used to support it as dofollow blog until last year. I am unable to control spam comments luring in this blog. As for now, there is an average of 20 comments per post. The numbers even higher even I disable the comment section on blogpost over dated over than a month. Definitely, dofollow blogs attracts visitors and active commentators on your blog which is an excellent way for new blogs or those who seeking for traffic. But, dofollow blogs needs extra attention. Each outgoing links from comment section need to be monitored. If the link goes to any pharma, adult, gambling, debt collection, etc which is not related to your post, then you might have the risk of lowering site quality.
Google have clearly state in Google webmaster blog that dofollow comments have the risk of reducing site’s quality. A well moderated dofollow blog have better quality compared to unmoderated dofollow blogs. Matt Cutts has agreed that dofollow commenting still flows some page rank value which may not help a lot. I would say yes if the post has hundreds of comments unmoderated and growing each day. But, if the post only has less than 10 comments and well moderated, then the pagerank flow is good. It would be better if the page gained some page rank value which will help increase our page rank as well. So, it is clear that dofollow blog commenting is still counted as quality back links that can increase Google SERP ranking and page rank if the blog post have low number of comments, moderated and high PR. Bloggers known method of socialize is commenting. So, if you have a blog and wanted to increase page rank, start commenting on dofollow blogs.