From the type of comments I receive daily (and I’m sure you do as well), two things are obvious.
1 – Either blog commenting still works OR
2 – It doesn’t work but people still believe and are trying.
Blog commenting is different from Blog spamming
Blog commenting in fact is a nice way to build traffic to your site, if you do it extensively and in the right manner with lot of focus. But what we see typically are not focused attempts, rather quick jobs where they plug in the primary keyword and write something random irrelevant to the website content. This is not blog commenting, but blog spamming.
The right way to build traffic through blog commenting
1 – Focused strategy
Spent a lot of time on the content, reading it, understanding what it is about. Do not copy paste your template replies like “Great content. Loved it!”. It easily will be detected for spam.
2 – Do not use meaningless terms as username
For getting anchor text benefit for the keyword, many people use their keyword itself as the username. Big mistake. Use only real names as much as possible. Additionally, you can add/tweak it to include the keyword may be, but leaving the keyword alone is a major put off.
Ex: Good name : Your Name (From this blog[Keyword])
Ex: Bad name : Keyword
3- Leave meaningful comments
Even if you left a bad username, it would be excused if you have a relevant comment. This is why reading the article is important. Write insightful comments and even if your username looked spammy it would be excused unless it’s a really bad name.
4 – You do not get link juice or text link advantage
Many a times, webmasters who do this are under the impression that a blog comment will work like a text link to them. No. It doesn’t. All you could get is some traffic. And that too only if you leave relevant comments. Mostly links are nofollowed on commenting platforms so don’t assume that you’re sourcing page rank.
5 – Comment on relevant articles that are related to your site/product
Okay, so you’re anyways trying to get some traffic and attention so rather than blindly commenting at top PR blogs, target those relevant ones that are related to your product. For example if you have an iPhone application to sell, google search related product reviews and forum discussions and comment there with insights on how your product is different or what you’re trying to do. Since the content there are already related to your product, whatever attention you get there would be relevant and will add value to you and the content source.
So essentially, the point is that blog commenting does not work as a link building method when you compare to other link building methods. However it can add value to your content if you place them cleverly on such platforms that can on a long term period give you attention. Blind blog commenting on various top PR blogs just to get link juice is an outdated idea. I wish if it worked.