To me, blog commenting is a unique way to connect with people in the industry. Why? Because leaving a comment is a great conversation starter. Further on, you can follow the person you're interested in on Twitter/Facebook/G+, exchange emails and what not.
Blog commenting is also an effective link building technique. While most blog links are nofollow, they can be great direct traffic channels at the same time. If you leave interesting comments, people will be eager to learn more about you and may click on the link in your name/signature.
Unspoken blog commenting rules
Just like any human activity, blog commenting has its rules and conventions. It's better to get familiar with those before you start commenting, to avoid learning the hard way and to avoid gaining bad reputation.
Here is a blog post we did on commenting etiquette some time ago. To sum it up, when you comment on somebody's post, make it real-life conversation. You wouldn't want a stranger to approach you and say something meaningless or begin selling you merchandise, would you? So, blog commenting is very much like starting a conversation in real life. Just keep that in mind. Read more »