I have several regular visitors who leave long and well-written comments. On occasion they would like to go back and modify the comment (especially the grammar teacher - she is mortified to publish anything not perfectly correct).
It turns out, however, the the ability to edit a comment is not based on he author of the comment, but the author of the post to which it is attached.
PLEASE add an edit_own_comments capability. I looked into writing a plugin to do this, but the hook at user_has_cap won't work because the call to
current_user_can('edit_post', $comment->comment_post_ID); has already obscured whether a post is being edited or a comment.
It seems completely natural that a different set of rules would apply for comment editing and post editing, but there is no support for that in WordPress.