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This regarding "Posting a comments in blog".
1)Can anyone help me about there importance of posting a comment in blogs and how we can get more back links.
2)If we post a comments in blogs along with url it shows rel=nofollow tag to the posted URL so, what is benefit of posting a link in comment box of blogs.
"nofollow" is an important part of that SE fightback against blog spam.
Keep posting: if you have something interesting to say, you may still get direct referrals - but not if you are a Canadian Pharmacy!*
*Joke, honest! :)
And I got advice here at WebmasterWorld that in order to grow your own blog's notability it's helpful to participate in your field's online community.