Blog commenting is good way, but beware of selecting blogs on your niche. Dont place link on cross niche blogs.
You are doing right. But in seo you can't depend on one thing only. You don't know which thing gave your work the perfect shape. Do some link building and social bookmarking etc.
Its actually the easiest way to have you site flagged as spam! I would mix your backlinks up a bit and not just use comments as your source of backlinks.