I do very much agree with Alex’s main point:
I think people do their best writing when they’re forced to defend their ideas on their own turf. It’s one thing to leave a comment on someone else’s blog, but quite another to put your argument in front of your own readers. It forces a level of consideration that, without fail, results in a higher quality exchange of ideas.
However, I think for a technical blog like this, it isn’t reasonable to expect people to post corrections to programming errors on their blog, or to send me links related to my posts via email. That barrier to entry is just to high, and as such, I am silencing some positive interaction. I agree that for any real debates, comments are not the right place. But for something small like a comment, they are just the right thing.
Maybe the right approach is to add a Twitter style length limit to comments?