On Slashdot (which I am likely dumber for reading) comment spam takes a slightly different form. Instead of earning PageRank, commenters earn karma. The end result is that instead of creating links to sites in order to screw with search engines, the spammers try to post good comments with the least amount of effort.
Take a comment on a new largest prime number for example. It sounds pretty good, but the tone of the comment is familiar; a rote collection of facts with a neutral point of view. Sure enough, I found the exact same text in the Wikipedia article on prime numbers.
While it’s questionable whether the comment adds value to the discussion, plagiarizing the Wikipedia is certainly deceitful. I guess whenever you create something of value like karma, some people will ignore social norms to do whatever they can to get it. Someone should come up with a name for that behavior, and then someone else should come along and add the word “freak” to the beginning of that name.