I think its depend with your commenting method. If you give a lot of commenting and over optimizations, I think this is only waste your time. Just keep and natural when you give blog commenting activities.
to increase the page and domain authority and to make it look natural, you should comment occasionally and consistently. i guess..
Since I do not have much experience in SEO, and since it was one of the first technique I learnt during my learning process, I am doing it. But I am trying to say something relevant and not to spam. Maybe later, when I have enough experience and find out that other techniques may be more successful and reliable, I will stop. It is true that it takes a lot of time to find the appropriate site, read the article and comment.
Blog commenting is getting more and more irrelevant.
More and more blogs are dropping comments section.
More and more blogs are getting very serious about spam.
All freaking spam!
Most of that spam are so called blog commenting services.
Best to not waste time and energy and money going to blogs and commenting.
Sami4u (21 March, 2013)