Bug 536 asks to save the last visited revision (LVR) for pages in the watchlist.
Enotif (bug 454) (or related patches?) already utilise this to show in
Special:Watchlist that a page has been changed since last visited.
A further enhancement would be if the watchlist could somehow be sorted by the
number of edits since the last visit. For this to be possible without heavy
database load, the number of edits should be stored in the table that records
which user watches which pages. It would be set to 0 every time the user visits
the page, and an edit to the page would increase the number for all