If you save a post it sends you a notification every time someone leaves a new comment, even if it's not a reply to you. I'm not sure how you use your save feature though; some people might not wish to save a post they are interested in following for only a day or so.
You can unsave a post any time you wish and the comment notification feature can be turned off if you are not interested in the comments. This is not on a per post basis tough. You either receive notifications or you don't.
Perhaps a 'subscribe to post' feature is in order, as another option for those who opt not to receive notifications?
It might sound weird, but I think that the all or nothing approach mk is taking here is actually a natural way to do this for Hubski. Hubski is a place for thoughtful discussions, so the article is not the main thing to have quick access to. The discussion is. And you either want to keep up to date with the discussion or you don't. If this isn't what you expect of a save function, you can turn the notifications off and you have a save function which only saves the articles and not so much the discussions that follow. This is my interpretation of the current save function, but only mk knows why he did what he did.