More evidence that "millions of people in the same room" isn't a sustainable model for online communities. I've been feeling for years that some kind of "chain of trust" and/or "X degrees of separation" reputation model is basically inevitable for broad-scale online social communities.
I suppose bots could find forums that use the most popular software and still make accounts and spam, but it would be much more obvious and less fruitful for someone to spam deck builders in Vancouver (something I saw often on Digg) on a forum that is focused on aquariums owners in the midwest.