It would be useful to have an option to prune unread alerts after a certain amount of time. Just noticed that I have some users with over 10,000 unread alerts because they are watching some very active forums, but they haven't visited the forum in over a year (their watched forum settings were imported from vB in case you are wondering how they are watching a forum for longer than the feature has been there). I have hundreds of users with over 1,000 unread alerts due to the same issue. How useful is an alert really to the user when the alert is from 6 months prior? And for scaling purposes, when you have someone getting alerts for every thread (or in some cases every post) in a forum for years and years when they don't visit the site any longer is going to end up with a lot of records in your database if you use XenForo for like 100 years or so.