Commenting on blogs can help your search rankings in two ways. Directly it creates links back to your site. As we know the more links you have the better, the stronger your site becomes. Some links may have effect on your search engines some links won’t, the ones that are nofollowed.
Indirectly commenting on other blogs can help people find your site and then inturn earn links. For example I found Joost de Valk’s website by a comment he made on another site. I now link to Joost’s website in my blog links.
The more visabilty you create on the internet the more people will start to link to you, that is if your content is good once their arrive at your site. So start commenting on blogs in your industry now, comment regardless of if the link is going to pass page rank or not and use anchor text that reflects your site best.