The comment box should have the option to edit a comment. Not just delete one.
The comments should also allow line and paragraph change (or what ever Shift+Enter and Enter are called, again). Currently they only add a space. Ideally a rich text editor of some sort would be nice. But at least line/para changes would be much appreciated.
Oh, and tagging another user with @Sandra or who ever one would want to ping/note/"cc"/etc.