I'm strongly with 'Zak here; there's little I hate more in the domain of Internet conversations than people deleting things their wrote. In fact, I believe there is a strong community interest in all (not killed by moderation) comments remaining up as long as the whole discussion exists. I don't mind if someone unlinks their post by e.g. deleting account; I care less about who wrote something than about what was written. Deleting posts ruins the discussion for those who come later.