Commenting on popular blogs is a great way to market your blog. It will be especially useful for a few reasons:
• It is a way to obtain new visitors. People often click on links to your webpage if you make an interesting comment. It is especially true if you are one of the first to do so.
• If you are posting on a do-follow blog, it is also going to improve your Page Rank, as it is going to count as a link. Obtaining links pointing to your site is crucial.
• Since popular blogs have really a lot of visitors, your comment might be viewed by thousands of people. That means that your blog is going to be more popular as well.
Most importantly make sure that you enjoy doing it.