This Is How We Roll asks the question and they identify three types of commenters.

The Troll – Everyone knows this guy (and it’s usually a guy), who intentionally visits sites in order to stir things up, provoke a furious reaction from other posters and then disappear. Classic examples are the Free Republic types who visit Daily Kos and vice versa.
The Droll – The mainstay of all fun sites, this poster regularly tosses out clever comments, plays on words, one-liners or amusing pictures. There are a lot of these characters on places like Fark.com

The Relentless Pol – Posters who can’t join any discussion without immediately using it to make a political point, i.e., “The current lack of sunspots is the direct result of the Bush administration’s failed policies.”

They point to this story at ABC which tackles this question.

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