For those of you who only comment on blogs in the hopes of including a link back to your website: beware. Savvy blog owners will read your blog comment like a hawk, and read the between the lines to decide if A. you actually read the blog post and B. if you are being legitimate. If the blogger treats "dofollows" like this guy, you're out of luck. See here where Google started to implement "nofollow tactics" to prevent this sort of thing. A "nofollow" command tells search engines like Google to not follow a link, and therefore not count it in the grand link popularity count for a web page, as seen by search engines.
What would be the most blatant attempt of using a website or blog that does allow comments to count links, is to inject a rel="dofollow" command in the code of your comment. Which doesn't even do anything. It's an attempt to override a "nofollow" command set on a website. Therefore, it's just salt in the wound of your attempt to create a link to your site, and calls attention to you even more. Blogger blogs set the "nofollow" by default, and WordPress.com blogs might (see here for a WordPress.org "nofollow" setting adjustment for blogs hosted on individual hosting accounts). But what we do do is monitor every single comment that gets placed on our blog or regular articles. When we see one that is blatantly spamming or link-dropping, and ads no value to the article at hand, we delete with a swift click. But that's not all we do.
We have mollom.com reading each and every entry. Mollom is a fantastic resource for not only blocking a lot of spammy comments that never even see the light of day on a blog or website, but if one slips through, it gives the blog owner the option of reporting it to Mollom, so that they can be on the lookout for that infringer's IP address, or other super power methods Mollom has. Ok, it's not super powers, but it is data crunching.