I recently posted a comment policy. I do not get that many comments now, but I did delete a comment recently asking for help on a code sample, so figured it would be worth elaborating on.
Comments are great, and I hope to get more, but with my participation on the stack exchange sites (and commenting on other blogs) I definitely see the need to take active moderation. This is not a big deal for the site so far (I rarely post anything controversial) but is really necessary for any blog generating a lot of comments.
My position is not quite extreme as Ed Tufte, e.g. I don’t plan on deleting a comment if I don’t like the content enough, but I will definitely delete off-topic comments and anything I find offensive. My position is more in line with Jeff Atwood’s thoughts, who discusses the topic quite a bit on his coding horror blog (see here for one example).
Basically the comments take curation, just like any site or wiki. Comments without moderation in any substantive amount (e.g. YouTube, many news articles) are simply not worth reading. The same moderation is what makes the stack exchange sites so much better than email list-serves, and the lack of moderation is what makes some MOOC forums so chaotic.