I've never used the ignore feature before, but since I needed to block som PMs, I went ahead and blocked all their content and I gotta say. I like it....if you don't have that nasty desire to actually see wtf they said, it really does work.
But I see why it's tempting...it shouldn't inform you of every single post....maybe the first post in a thread but when you're dealing with a spammer, it does kinda fuck up the flow.