When checking/unchecking the "Notify daily of any new answers" on a question that has already been asked, there is nothing to give the user feedback that the check has been registered. An AJAX event is fired to store the check, but the user doesn't realize that and goes looking for some kind of submit button, or maybe realizes it is AJAX but doesn't know if it was successful.
Typically, some kind of "working..." animation would display beside the field when the Ajax event is fired, and upon completion it would either disappear or be replaced with a green check icon or text saying something like "setting stored".
Note: I found at least two support requests on MSO from users confused by this:
