Marco Arment, of Instapaper and Build and Analyze fame, recently had a blog post entitled "Why I don't have comments on my site." He was responding to an insane, rambling rant of a comment on The Verge (which he reproduces in its entirety in his blog post). The comment, to the extent anyone can follow it, complains that Mr. Arment doesn't know "real" programming languages and is an Apple "fanboy" before an abrupt lane change into a paragraph on "stolen open source projects."
Although he doesn't say so explicitly, Mr. Arment's implication seems to be that having comments enabled leads to these kinds of comments, which then either require time-consuming responses or just leaving the rambling unrebutted. He's a professional software developer and spare-time blogger, so I understand that he doesn't have time for the first option and that the second option is unattractive.
I'll venture a guess that most bloggers share my opinion that comments are a wonderful thing. Most of us don't have a big audience and are happy to have evidence that someone out there is reading. Better than that, really: not only did someone read, but he or she took the time to share some thoughts with the author. I don't care how cranky the response - the cliche that it's better to be talked about than forgotten applies amain here. (Spammers, I make an exception for you. Begone.)
Blogging is clearly one tool in a professional's kit, a way to communicate with the public about one's product, whether that's a piece of software, series of science fiction novels, or a motivational speaking seminar. As such, people can choose the degree of desired interaction and, for those with big enough audiences, one-way communication might be the right approach. As for me, however, comment away.