One glaring deficiency in the watch system is its inability to cover categories.
Currently, when a user is watching a category, she will only get notified when someone edits the category page itself.
However, what a reasonable user expects, is to be notified whenever the "category page" changes, in other words, whenever a new page is added or removed from the category, or whenever a page that belongs to the category gets renamed.
a separate level of notification might be "whenever a page belonging to the category is modified", but if we want to support this, it needs to be controlled separately from the main thing, which is, to be notified when the content of the category changes. what i mean is, "watch the category" and "watch all the pages in category" should be two separate controls, and a user can choose one or the other (or both).
Please note that "watch all pages in category" should *not* be implemented by adding all the pages in the category to the watchlist: first, this will not cover pages who acquired the category after the user added the cat. to her watchlist, and 2nd, it is very much possible that the user was already watching some of these pages, then decides to watch the whole category, then decides that it's too much and removes the category watch. she should not lose the individual pages she was watching before.
peace.