How should I handle comments?
Comments are—for the most part—intended to be ephemeral bits of information used to improve the quality of the post they're found on. If they aren't contributing to that, they generally don't belong.
If you see an ongoing discussion or argument in the comments of a post, consider stepping in and asking the parties involved to roll the fruits of the discussion into the post and take the rest of the conversation to chat. Once resolved, consider cleaning up the comment chain.
If you see personal attacks being thrown in comments, or other unacceptable behavior, delete the comments on sight and consider taking additional action, like warning the parties involved.
Can I migrate comments to chat, or another place?
Yes: from the post's 'mod' menu, select 'move comments to chat'. Bear in mind that this can only be done once - if the discussion continues in comments after you've moved it to chat, your only options are to delete the comments, edit them, comment yourself, or lock the post (see below). Also remember, users who are part of a back-and-forth chain of comments are given the option to migrate the conversation to chat themselves, if all of them have the chat privilege (20 rep).
Can I prevent users from commenting on a certain post?
You can lock the post with the reason "off-topic comments", which prompts users to go to chat for further comments. Note that this will also prevent the post from being edited, and if applied to a question, will prevent others from posting answers. This should only be done as a last resort, if all other attempts to moderate a comment chain have failed, or if the post continues to attract comment chains or unconstructive comments over a long period of time. You should also set it so it unlocks after a period of time.
Unfortunately, there is currently no way to only prevent commenting without the other ramifications of locking, so use this very sparingly.
Should all comments be deleted when cleaning up a large comment chain?
While comments in general are not supposed to be permanent artifacts, consider leaving comments that link to related resources or clarify a small, tangential point in the post. On questions, also consider leaving comments prompting the asker for information that has not been addressed yet.
Can I undo a comment deletion?
Comments can now be undeleted, but only if they were deleted by a user who is currently a moderator. The reason behind this rule is because moderators should only be able to undelete comments deleted by moderators, not by the comment authors themselves.
This does have a few holes, however: if a comment was deleted by a moderator who later lost their moderator privileges, you can't undelete it. Also, as comments that are automatically deleted in response to flags have their deletion attributed to the last user to flag, you can't undelete those.
...After deletion, the standard "deleted content" styles will show the just-deleted comment, along with the "undelete" link.
Also, the "X deleted comments" right side-bar quick link will now load deleted comments inline, allowing for undeletion (in certain cases)
Can I see what comments have been deleted?
To see all the deleted comments on a post, click the
mod link, then select
show deleted comments. To see them with the undelete link, click the "X deleted comments" box and the deleted comments will appear inline on the post