[shostack]

Other responses covered the basics, but there are a few other interesting uses.

- Text that does not clearly market anything or provide a meaningful backlink may be part of a larger link network, or just simply testing to generate a list of vulnerable blogs. Those lists can be sold to others or used for your own purposes.

- Similar to some recent spam bots hitting Google Analytics referrer results, these people may not care about organic rankings. They might be marketing to the blog owner who sees the comment and investigates the username/link. If I'm spamming for SEO services, and you are a blog owner looking to increase traffic for example, the attempt may not be about ranking for SEO terms (a losing battle), but simply getting you to look at my site.