>All NNTP readers store information about read/unread messages localy so there's no extra load on server. I think it'll be overkill to store such info per user/message on the UT server. I would suggest that whatever mechanism you've now to ditinguish between read/unread messages for a user should be implemented per user and forum combination.
I understand that the amount of information would be huge. But, as we don't have any client, we cannot rely on local data. For now, we have a last read date per forum. This is how it has been done so far. What you propose, is also what I have been thinking tonight as a flag to reading new messages. Basically, assuming all forums would be collapsed, as soon as one would be expand, we could trigger an update of that timestamp. We could also add the number of messages per forum in the forum title. So, as long as the forum is not expanded, those new messages will remain as new. I'm not sure this is a setting that would fit all however.