Topics are only split when the discussion diverges enough from the original points, the follow-on discussion is noteworthy, and the moderator believes the (new) subject deserves its own thread. Although it's an interesting suggestion, meeting all of these criteria doesn't occur frequently enough to justify propagating watched topic lists to follow-on discussions. For now, the moderator provides back reference pointers and interested members can click Watch this topic for replies, if they wish.

As an aside, it may become necessary to "expire" members' watched topic lists from time-to-time. HB is on a shared server and too many outgoing e-mails falsely flags the server as compromised by a spammer virus, resulting in all outgoing e-mail access being suspended for 24 hours. It's only happened once in the site's history, but it's on my idle time to-do list. The easiest solution would be to expire the watch topic lists for those who haven't logged in for 60 days.

Sure, but if someone hasn't logged in for over 60 days, they probably don't care about nicely worded notifications. The notification expiration is really directed towards those who sign up, ask a few questions, then vanish into the Internet ether. I figure that if someone hasn't signed on for 2-4 months, they're probably never coming back.