Yesterday I made some improvements to the board's system of tracking read/unread threads, so I guess I should make a post about it...
Up until now, the board stored info about threads you've read in a cookie, and that cookie had a limit of 40 threads. Now the info is stored in the database, same as in MyBB 1.2, so the board can remember an unlimited* number of threads.
* Records older than 2 weeks will be pruned to keep the size down.
Also, I added a useful option that tells the board to ignore your last visit time, so threads won't be marked as read just because you closed your browser for 15 minutes. You can enable that here:
http://shoutbox.menthix.net/latest.php?action=configread
(The option only applies to latest.php and forumdisplay.php at the moment, not index.php. Forums may be marked "read" even when they contain "unread" threads.)