[eluser]jedd[/eluser]
Yeah, I do like the idea that it's based on thread, rather than messages.
I've been pondering Fuzzy's suggestion of a fixed number of rows, created at user-creation time I guess, that you can use for this purpose - the attractive aspect of that is that you don't end up with (too much) cruft in your db.
I guess the other features that need to be considered is the ability to
relatively inexpensively identify who should get notified when a new message pops up in a thread. Each way I look at it, the SQL seems to be non-trivial to do this, mostly because of the presence of cruft I expect. I suspect I'll need a comparably designed table to record thread/user/notify correlations, and tie into that at the same time.