I don't really mind the paid comments. As long as they pertain to my post and I don't disagree with what their link is peddling, I will approve it. I won't visit the site myself (unless it's to check on what it is), but if they are willing to take the time to post a real comment and someone else that sees my blog wants to click on their link, I don't see why it should bother me.
My recent post 8 Ways To Stop Me From Reading Your Blog