I comment on numerous websites and, of course, many peopl comment on my own. In my own case, my commenting is motivated by a desire to add to the discussion of the topic. I very often think by means of writing on a topic, and commenting gets my brain flowing. These comments often result in blog posts. But as Amy Gahran notes, nt every comment is motivated by discussion. A significant number of them are intended only to attract business or website traffic. Though not technically the vile weblog comment spam, these comments are still unwelcome. "As if my blog only existed as a springboard for his marketing!"