It seems to be a dead practice and not worth the time. Note, the past fashion of do-follow commenting had become spammy, hence the recent negativity associated with the practice.
Blog commenting doesn't worth too much in today's seo, however it still a good way to get some online reputation, network with other bloggers and increase social signals.
Forget about blog commenting because its not a method for optimizing a website but focus more on your content.
Blogs are not social sites like Twitter - so don't waste your time thinking it will boost your rep - it can't due to the only ones using blogs are infact more spammers looking to get a free link. If a blog publisher deals with 500 posts a day/week, chances are its 90% spam - of which will be deleted. If it looks like spam, smells like spam - guess what.... Desperate fools...
Blogs are web 2.0 properties, if you comment on good blogs and you add valuable information not just trying to get a spammy link, it may help your reputation online. Try to add value and write great comments with critical point of view or complementary information not those crap comment with no added value for the blog owner and readers.
Even with good content intentions - no one person can post enough to stand out, the web is too vast for this ancient method to work. Besides, comment forms are so over used by spammers, the mere knowledge of the activity frightened every blog to no-follow such links giving zero value, making the activity worthless.
I would do it on big blogs and if you post some good comments you will get visitors to your site that can convert if done right. but it really provides no SEO juice.
Blog commenting does not have any SEO weightage in these days. However it is very effective in driving quality visitors to your blog. I am also doing blog commenting and it help me to get quality readers for my blog.
I am still doing blog commenting, but of course with quality and related content. Be Good SEOer not spammer
Blog commenting is dead as a dodo - Google devalued them and too many blogs no-followed themselves to the point that 'posting comments for link boosting rankings' is wasted effort. Only the clueless desperados waste time doing this, and the only traffic blogs get is other comment posters looking to spam.
Not always blog commenting is good for SEO. You need to find out whether the commenting blog holds quality traffic or not. If Yes, then comment to leave your internal links or category links of the website or blog which will help you to rank in the Google Search Engine.
Do people research anything before starting a website , then come on forums convinced their MFA (made for adsense/affiliate) site works, looking for others to make them successful. Let me tell you something for free - no one will help you ever. The weak marketing tips offered on forums wouldn't supply sales to buy a loaf of bread, never mind - oh god I cant even be bothered to explain why such laughable free resources/methods fail. SEO is the biggest con-job ever invented. If you need to hunt/ask for help, then clearly the website you own doesn't work and likely never will. Sorry, its just the way it is. (Btw - Following certain threads and plugging your bad advice isn't helpful - you need to stop this.)