I have set all comments on my blog to DoFollow. Or rather, since "DoFollow" is not really a term (whatever others might say), I have removed the nofollow attribute from comments on this blog. Some may wonder what is this DoFollow and nofollow (what....no capital letters in this one) business. Basically, most (by which I mean 99.99999%) blogs and social networks use a nofollow attribute in their comments to counter the intrusive spam that has become the signature of the Internet.
Nofollow means that links will not be crawled by Google and other engines as it essentially tells them to discard this link and that the blog owner is not endorsing it (get it; no follow....don't follow). Several years back, this was not a necessity as the need for search engine optimization and linkbuilding had not yet exploded. People were not crawling the web looking for blogs to spam on and links that were included in comments actually counted as a backlink.
However, once it became essential for websites to have backlinks to rank in the first page of search engine results page, these same blogs were suddenly the target of spammers who would simply post tons of links to their websites on all the blogs they could find. This usually amounted to using their keywords as their name along with the link to their website, but others would go a step further by just listing several links, especially porn and gambling sites, in a comment. Eventually, with tons of people posting so many comments on a single blog for that precious backlink, it became difficult for webmasters to moderate these comments.
Thus, when the nofollow rule was implemented, webmasters were glad because this meant they would not have to wade through 50 "free viagra" comments per day and just one comment pertinent to that post.
Except that's not what really happened. Spammers are still crawling the net, looking for blogs to abuse, even when these are nofollow. They probably did not notice that they were wasting everybody's time. They were wasting their own time because they would not actually be getting a backlink and most people were going to ignore their irritating "SEO Experts Free Advice" link anyway. They were also wasting the blogger's time, who still had to go through a lengthy moderation routine on a regular basis. And those comments that the blogger may have decided to let through were wasting the time of those readers who actually cared about the content.
Based on this, I have come to the conclusion that it does not matter whether a blog is set to nofollow or not. For one thing, I do not believe that a single nofollow link is going to make such a big difference in your ranking. My blog currently has a PageRank of 2 (not that PageRank matters, but some people still seem to think it's the only thing that matters), but even if a blog with a PageRank of 6 set its comments to DoFollow, the effect of posting your link as a comment would be quite minimal. And I'm not going over the fact that the post itself would most probably be completely unrelated to the backlink (as in a "Casino, win big money" link on a post detailing why Wayne Rooney is going to have a forgettable season in the Premier League this year).
This is why I have just edited my blog's source code to remove the nofollow attribute from comments. It will be interesting to see how many spam posts I get as a result, but I'm willing to take the risk.