Joel has some interesting comments on comments:
The important thing to notice here is that Dave does not see blog comments as productive to the free exchange of ideas. They are a part of the problem, not the solution. You don't have a right to post your thoughts at the bottom of someone else's thoughts. That's not freedom of expression, that's an infringement on their freedom of expression. Get your own space, write compelling things, and if your ideas are smart, they'll be linked to, and Google will notice, and you'll move up in PageRank, and you'll have influence and your ideas will have power.
Joel's point seems like a sane one - if you agree or disagree with a post the right thing to do is to express your own thoughts in your own space. Seeing as starting a blog is so easy, it shouldn't take much to do this.
Personally, I like comments on my blog. They give me an opportunity to easily poll my readers and to make my posts somewhat interactive. Oh, and they show that at least someone is reading what I'm writing.
Still, I'd take this suggestion as yet another reason to start a blog. So go, get cracking.