It's Spam But yes it still valuable for google and bing.

Let me be clear on this one. First of all most of the blogs provide no-follow links and the least amount which actually do provides do-follow links passes no value at all. So, if you are doing blog commenting to get ranked then it will get you nowhere.

Although if your comment provide some value then you might get some referral traffic out of it but that's it.

If you are leaving a comment on a blog for the purpose of gaining a link, you are a spammer. End of story.

The proof is the thousands of websites who spent years building spam comment links who saw their #1 rankings disappear overnight and their rankings drop to #100 or worse when the Penguin algorithm filter was launched in 2012. Penguin has gotten even better at filtering out spam blog comments every year since then.

But go ahead, spam away! If nothing else, it will make it seem like you are working on something important!

1. All blog comments are spam.
2. In case you think your comment is not spam, refer to #1.

Nofollow has nothing to do with spam, or any other such nonsense.

In fact, google has said don't do ultra-idiotic-anchor-text in forum sigs. No matter that they are nofollow. Google is not blind.

You want to comment in a truly hidden way, then do FB plugin commenting. A beautiful way to pump up traffic, sales, shares, etc. Here's a hint. Numerous newspapers use that as commenting.

Oh and BTW, yahoo is now (in certain articles and blogs), allowing links with image preview exactly like FB plugin. Nothing to do with seo, but hey, I spend a vast amount of time getting MY OWN traffic.

Paul