Matt mentioned the (old) Rachel Corrie thread, and I couldn't help but notice something informative about it. The first three pages were more or less dominated by anti-Zionists, and they appeared to use their flagging abilities to overwhelm comments that they didn't like and get them deleted. This wouldn't be notable, as that is the way the Huffington Post system works, but the result is a very obvious wasteland in which every third comment is removed while obvious insults remain. You can see this now if you set the thread to "favorites." Here are some examples:
Fortunately this trend ended quickly.