If you are not familiar with what comment links are, allow me to explain. A comment link is the practice of going to another website and leaving a link back to your site in the comments section. You can do this by filling out the comment form.
This video by Matt Cutt’s surprised me a little. Basically, comment links are not spam when done correctly. Cutt’s advises that it is best not to use keyword heavy anchor text and also best not to go nuts with commenting on other sites all the time. However, comment links are still OK and can be done in a respective way and still be effective.