I know Stackoverflow is wisely trying to avoid an excessive notification system (like's facebook's, but I would definitely like to know when somebody responded directly to me. Since we're already notified when someone comments on our question/answer, this would be for when someone responds to my comment. I sometimes ask questions or express opinions in comments, and I would love to know when someone responds.
Normally, you only get notified of comments when you own the post.
You will now get notified of any comments that refer to you by @username in a comment, even if you do not own the post.
This isn't really possible at the moment for two reasons:
Personally I think this kind of thing just needs to be handled by a subscription model something like this
You should be able to opt-out at any time ("unsubscribe") from these notifications. Likewise you should be able to opt-in ("subscribe") to something like: