I just noticed that the sitemap does not update after I edit an existing comment. I know this is an issue with the way comments are stored in the database, but it would be great if it were possible to update the timestamp when comments are editing. This is useful if say someone posts a junk post and Google spiders it before the admin can edit it. If it has already been picked up and then edited, it doesn't show that the node has changed since the comment was created. Hope that makes sense.