Do-follow is a word which doesn't exist . however it is used as a word meaning the opposite of No-follow Do-follow is nothing but a tag which tells the Search Engines to Crawl Through it and thus increases your frequency of SE's crawling and it also helps in the Search Engine Optimization (SEO) . Where as The No-Follow tag doesn't allow search engines to crawl through the link. No-follow doesn't Harm the SEO of the site until and unless there are too many
If done wrong you can end up on the akismet list real quick and then commenting will become almost impossible. Careful to keep comments on subject and use a real name with your link text.
Dofollow blog commenting is one of the most powerful way to obtain backlinks on the Internet for a little effort of commenting usefully
There are a few discussion threads whereby the participants compile a list of dofollow blogs. However, the best is to comment on blogs relating to your niche, regardless of dofollow or not. If you manage to find many dofollow blogs in the same niche, that's good. If not, just leave comments on the blogs. You probably get traffic as well.
I wouldn't recommend using Do follow links just because this takes away from your search engine and backlink juices. See my article I wrote here for more information.
There are a lot of lists of dofollow blogs, but I find most outdated. Sadly, the reason is people install dofollow plugins just to get listed and get some hight traffic, then just disable plugins. Also commenting on those blogs might not be so efficient since, they tend to have tons of outgoing links, and this means less juice for you.
Do follow Blog commenting is useful in google, yahoo and bing No follow commenting useful in yahoo and bing
To get backlink and increasing PR, it is the best way to get that...but sometimes who need backlink doesn't know anything about respect, so they often spam it...It's just a myth when we change our no-follow to do-follow that losing our PR...
Do follow blog is very usefull because it give a link back to our website. But please do not give spam comment, we must know the unwritten rules also.