Well, blog commenting is a very useful activity of getting some valuable and quality back links from some other website but the important thing in blog commenting is that your comment should be very strong and very informative and should also be relevant to the post too so that you can get traffic as well back links too...
Blog commenting does work... Just avoid spammed blogs with many other links... Don't bother with writing too long comment, waste of time... and don't expect any visits from commenting. It is mainly for SEO.
I haven't done it long enough to have sufficient proof whether blog comments do or don't help SEO. But I do notice that many blogs have nofollows due to spammers, and that defeats the purpose of commenting for anchor text placements.
I want to add another point: blog comment do brings traffic, even spam, when admin process the spam, they will come check your site. For approved comments, it bring many(not lots) traffic.
What I found very useful are the discussion forum after the comments on the blog are my best source of online traffic
If your competition ranks organically higher than you and has more blog comment links that's your answer. I'm looking for some one to do blog commenting for me.
Are talking links in the body of the comment or attaching to the poster name? If the latter, getting onto top-commenter lists can give a good number of backlinks.