Commenting on blogs is one of the better ways to build inbound links to your website.  Aside from incoming links, it also gives you other things such as brand presence or publicity, reputation and more visitors.  You don’t have to overdo it to be effective.  Leaving a comment on at least 2 or 3 different blogs a day can still be as effective if done diligently.  At a rate of 3 comments a day, you’ll have 20 or so made in a week.  That’s already 20 incoming links to your site!