Here's an interesting discussion in a church blog on the subject of allowing comments.
Comments give us flames, trolls, comment spam. Imagine: if the left took some of the hours and hours of work they spent last October fighting comment spam and trolls on Atrios and DailyKos, and spent maybe a tenth of those hours canvassing Ohio and Florida.
Moral of the Great Weblog Comment Experiment: comments build traffic, but not traffic you want or you can use. Link liberally to other weblogs -- including those that disagree with you -- but let your opponents publish in their own space.