I participate in the http://mangolassi.it community and just noticed that if you hover over the "replied about 18 hours ago" text, you see the actual timestamp. Great little gem. Can it be set to show something more readable though?
I think this is plugin territory. In my forum I have several threads where only admins can post updates for users. Not really a discussion topic, more of a change log or mini blog. If posts were to start merging the updates would get tangled.
Just one use case, but I'd prefer the core code not to automatically join double posts....or at least make it an option.