TNH on AW re: Comment moderation
http://www.absolutewrite.com/forums/showpost.php?p=3582777&postcount=18
Comments posted with obvious bad intent? You delete them as soon as possible. Letting them stand damages the conversation, and makes your site seem less worthwhile to the sort of commenters you want to attract. Next, you check their IP address to see whether they’ve made other comments on your site. If they have, consider deleting or disemvowelling those as well. Useful, substantive comments can be let stand, but if they’re just throwaways, zap them too. If you think your other commenters will be confused by this, leave a note explaining what you did.