I'm not sure if this has been suggested before, but I feel like thread subscription would be a very handy feature. Being able to subscribe to threads is basically bookmarking them within the site, so people can easily find them again. It's especially helpful during times where a thread owner doesn't always ping a person when they reply, because who knows how far down the list it went? As much as website bookmarks does help, it can get a bit much if you have a lot of threads you follow at a time. And, in the case of thread subscriptions, it would tell you on the subscriptions page if there were new massages, rather then having to guess.