Blog Commenting is a good way to get back link but blog must have good PR and our discussion must be descriptive and useful for someone.
Spaming changed the aspect of every thing in seo.What ever you do you think how you can do some more stuffing etc ,this is the thinking now a days that why search engines going so strict on the other hand Commenting is about posting your review on the blog content.Blogger is of google means by putting here a link will help you out in the search engines backlinks
Doing Comment posting is good for generating traffic but in a proper manner. While you are doing the posting it doesn't means that you always place you link in comment, whenever you think that you are providing the good information to the visitors related to that blog than only place your link else not. If you are doing spamming than Google close your account and sometime blog owner remove your links also which affect your seo work and ranking also.
The search engines still love blogs even after Panda, but it's always a good idea to leave a valuable comment with your blog commenting, or else it might simply be removed
The most important thing in blog commenting is that you give valuable comments. If not, it looks like you're spamming.
Blog commenting is one method to increase pagerank and get more business.It help to get more traffic and more visitors.
According to me, you should comment on relevant blogs. Don't comment too much otherwise u'll marked as spam.