There's a good interview with Torill on Netwoman where she sums up many of my own thoughts and feelings about Blog Commenting:

"TM: I don't have comments, because I have the blog for myself and my own pleasure. If others like to read it, I am very happy about that. If others want to discuss issues with me, I am exstatic. If they want to tell me how I should do things, I get unhappy and angry. Not having a comment-box and making people click a couple of times to find my email slows the response rate and sorts away most comments, but the comments I do get are are largely nice, friendly or genuinely interested in a topic. Those I love, and disagreement is no big deal. The unkind - I have had a couple that were snotty and one very unpleasant stalker, that's all."

In addition there are also the issues on comment maintenance - I just don't have time to be dealing with trolls, spam, etc.