I assume a whole new watching system would be needed for this, or at least a very heavily modified one. Therefore a wish like this would take a long time to implement, but would benefit everyone - particularly new users.

These features should be available:

1. A watch button, that allows the wiki creator to define which pages to watch when the button is clicked, and with customisable text:

• Pages by fullname
• Pages by category
• Pages by parent
• Pages by tags
• Pages in a category, based on their pagepath value?
• … allowing a combination of the above would be a massive bonus

Read more. This button could be used for blogs (category="blog") instead of the Watchers module, or for databases and other collections of information: allowing people to watch a certain tag or pagepath value to be notified about only those items they are interested in.

An example would be using pagepath by author of a computer application on RoaringApps.com - people can then watch for more apps from that author and be notified if any of that author's apps are edited. At the moment they have to manually watch each individual page, or the whole category. This isn't a friendly User Experience!

rurwin: The button should also, along with the customisable text that is shown on the wiki page, have a separate label or description of some kind that is to be shown in the user's watching dashboard. For example:
[[button watch text="Watch sport-related blog posts!" category="blog" tags="sport" description="John Doe's blog: Sport"]]
For each group of watching notifications, the user would see this description, a link to unwatch, and (as a bonus, see #4 below) a link to change the frequency that notifications are sent out via e-mail.

2. Anything that can be watched using the new watching system should also have a corresponding RSS feed address. (This may already be implemented well enough - RSS feeds are already very powerful as-is)

3. The ability to watch individual forum threads (built-in forum). Read more.

4. Watching notifications should be configurable:

• As it is now - instant notifications
• Summary email every 24 hours
• Summary email every week
• … allowing this to be specified on a per-site basis would be a massive bonus

5. A module that can be inserted into any page on a site, and will show a signed-in viewer of the page which pages on that site they are currently watching. This module should also allow them to unwatch pages.

More?
Anything else that you can think of? Suggest in comments if you have further ideas/suggestions. The overall wish is: improving how Watching notifications work, because they aren't quite as good as they could be at the moment.