There has been some discussion about getting notified on comments to questions or answers that don't belong to you, and the long-standing wish to be able to keep track of new answers or developments in questions asked by other people.
Previous discussion in regards to subscribing to questions:
In regards to subscribing to comments:
The general feeling - at least here on meta - seems to be against broadening the notification rules, out of fears of useless notifications to flood users' inboxes, turning SO into more of a discussion forum than it should be, etc.
Here's a suggestion that would keep the user 100% in control what they get notified about, not generate any notifications by default, and require only minimal modifications to the User Interface.
Each question and each comment area would get an envelope symbol.
it is inactive (=white) by default.
When those envelopes are hovered over, the tooltip says
click to subscribe or something.
When clicked on, the envelope lights up in green or some other colour (but different from the actual notification envelope's orange to avoid confusion.) You are then subscribed to any updates to that question or comment thread.
For each subscription, you receive notifications in the "responses" tab, as if you were the owner of the comment or question.
To unsubscribe from a question or comment thread, you open the page, and click the green envelope. It turns back white, and the notifications disappear from your responses tab (if technically possible - otherwise, there just won't be any new ones added.)
No further functionality, like managing subscriptions or anything, is necessary IMO. If the flood of notifications from a subscribed question starts to annoy you, you just open it and unclick the envelope. Done.
It would make it possible to leave a comment to a newbie's question and make sure their answer reaches you even if they don't know they need to address you using
You could subscribe to those "oh, I'd like to know the answer to that" questions and receive active notification, instead of them getting forgotten in your favourites list
You could subscribe to discussions you are interested in the outcome of, but don't want to participate in.
It would (in my opinion) sort out a number of woes aired by many users in a good way, without adding annoyances to those who like the system just fine the way it is.
It would not require a change in the visible layout. As far as I can see, the space the envelope would need to be is empty everywhere.
I don't know SO under the hood of course, but technically, the system would be doing what it's doing already, notify question owners of updates - just that the circle of internal "owners" would grow.