I agree with you that a filter function would be handy. I posted frequently on "Salon" for a year or so, and I found there was always the 5% that regarded discourse as a weapon. One gay-rights fascist went so far as to describe himself as a gay terrorist, and posted offensive links to people. I filtered him, which put him at some pains to get his trash in front of my eyeballs.
On Free Republic, I have only seen one or two people get that obnoxious.
And btw, "abuse" isn't the same as being annoying, and most people know the difference, I think. I don't think having an ENUF filter (as "Salon" called it) will eliminate calls to the moderator for truly egregious posts.