I am sure you have come across this question as often as I have in the affiliate marketing forums.
And it's a valid question. Because it takes time to compose a blog comment that will pass scrutiny and get approved by the blogs moderators. You have to read the post first and some posts are just long and then compose your comment. So if it does not work then blog commenting could be a total waste of time.
Before I go further, I must admit that blog commenting is not my main method of generating do follow links to my sites. it's not even a method that I spend a lot of time on these days.
I tend to do a lot of competition analysis and take my cue from there.
or analyze backlinks of the websites that I know are run by SEO 'gurus' and see what they are doing
Anyway during one of my 'guru' analysis I found a webpage that is doing pretty well in Google for a few decent keywords
And doing some backlink analysis found that the majority of the do follow backlinks to that page were.... you guessed it, blog comments
What really amazed me was some of the blog pages the comments were on had decent page rank. No not the home page, the specific post page.
So I think maybe blog commenting is not a total waste of time after all.
See you on the blogs :)