ExtendedComments and CommentTitles are coming along well so far. I am still working up the preview portion of the comment system, but as long as you just go ahead and post, it is working just fine. Once I get preview working, CommentThreads should follow up shortly afterwards.
Update (at 1:40 on 06/08): Okay, so I got preview working now. I was expecting it to go quickly, but not that quickly.
Cool stuff, but awefully confusing at first.